SEARCH · Search PubMed
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Three complete cDNA clones encoding Id-related helix-loop-helix (HLH) proteins lacking a basic region were isolated from a pcD2 cDNA expression library prepared from TIG-3 human diploid fibroblasts (HDF). Of these cDNAs (Id-1H, Id-1H', and Id-2H), two (Id-1H and Id-1H') appeared to be derived by alternative RNA splicing. Id-1H and Id-2H seem to be human homologues of mouse Id-1 and Id-2, respectively, and have potential to encode 154 and 135 amino acid proteins. The Id-1H and Id-2H mRNAs were barely detectable in quiescent early passage HDF; serum coordinately induced both mRNAs, with two peaks of expression, in early and late in G1. Antisense oligomers complementary to Id-1H and Id-2H mRNA prevented early passage HDF from entering the S phase of the cell cycle. The treatment of serum-stimulated early passage cells with the antisense Id-1H oligomer completely abolished Id-1H. In senescent cells, serum barely induced the Id-1H and Id-2H mRNAs, although the levels of c-myc expression induced were similar in early passage and senescent cells. The expression levels of these Id genes vary among immortal human cell lines. Both genes were overexpressed in VA4 SV40-transformed lung fibroblasts and EJ-1 bladder carcinoma cells, while these genes were expressed at a very low level in SVts8 cells derived from SV40 tsA-transformed TIG-3 cells. SVts8 cells may acquire some function redundant to Id proteins. HT1080 fibrosarcoma cells expressed the Id-1H gene but not the Id-2H gene, suggesting these Id genes may subserve redundant functions.
BACKGROUND & OBJECTIVE: Idiotypic immunoglobin (Id) derived from B-cell lymphoma, as a tumor-specific antigen, can suppress tumor development by inducing immune response. This study was to confirm the presence of Id epitope on cytotoxic T lymphocytes (Id-CTL) in mouse lymphoma cell line A20, detect the quantity and distribution of cell-penetrating peptide-loaded Id (CPP-Id) in dendritic cells (DCs) at different time points, and explore its impact on the expression of surface molecules on DCs. METHODS: Id-CTL epitope in A20 cells was amplified by reverse transcription-polymerase chain reaction (RT-PCR) and sequenced. The quantity of CPP-Id and Id alone in DCs and the expression of DC surface molecules were detected by flow cytometry. The process of CPP-Id entering DCs was observed under confocal microscope, and its distribution was observed under fluorescent microscope. RESULTS: A 660 bp-length fragment was amplified from A20 cells by RT-PCR, and identified as Id-CTL epitope by sequencing. CPP-Id entered DCs quickly during the initial 200 s, but few Id entered DCs. The mean fluorescent intensity (MFI) in DCs was significantly higher in CPP-Id group than in Id group (4.35+/-0.48 vs. 1.14+/-0.33, P<0.005). The expression of surface molecules CD80, CD86, CD54 and MHC-I, MHC-II were higher on the DCs loaded by either CPP-Id or Id alone than on immature DCs. CONCLUSIONS: CPP can enhance the quantity of Id entering DCs. CPP-Id can up-regulate the expression of MHC I, MHC-II and CD80, CD86, and CD54 on DCs, and may help to activate CTLs.
Overexpression of the helix-loop-helix protein Id-1 has been reported in over 20 types of cancer. While a number of factors have been demonstrated to regulate Id-1 gene transcription, little is known about the mechanisms responsible for its degradation. In this study, we have demonstrated that Id-1 protein stability was regulated by TNFalpha in prostate cancer cells. We found that exposure of prostate cancer cell lines, DU145 and PC-3, to TNFalpha resulted in a rapid and significant downregulation of the Id-1 protein level. The fact that neither the Id-1 promoter activity nor the Id-1 mRNA level was affected by the TNFalpha treatment suggested that the decrease in Id-1 protein was not due to the suppression of gene transcription. In addition, the half-life of the Id-1 protein was decreased in both cell lines in the presence of TNFalpha, and the addition of an ubiquitin/proteasome inhibitor (MG-132) prior to the TNFalpha treatment completely blocked the effect of the TNFalpha-induced Id-1 protein degradation. Furthermore, introduction of a Flag-tag sequence into the N-terminus region of the Id-1 protein, which has been shown to stabilize the protein, was able to protect the Id-1 protein from TNFalpha-induced degradation. These results suggest that TNFalpha downregulated Id-1 through activation of the ubiquitin/proteasome degradation pathway in prostate cancer cells. Interestingly, in both DU145 and PC-3 cells, the decrease of Id-1 protein was associated with the activation of apoptotic pathway, as evidenced by the increased expression of cleaved PARP and caspase 3. In addition, TNFalpha failed to downregulate Id-1 in a sub-line of LNCaP cells that was resistant to TNFalpha-induced apoptosis. These results further suggest that the downregulation of Id-1 may facilitate TNFalpha-induced apoptosis in prostate cancer cells. In conclusion, our findings indicate that Id-1 protein may be regulated by TNFalpha through the ubiquitin/proteasome degradation pathway and the stability of the Id-1 protein appears to correlate with the sensitivity of TNFalpha-induced apoptosis.
BACKGROUND: Members of the Id helix-loop-helix proteins are key regulators of cell growth and differentiation in a variety of cell types. They are also required for cell cycle progression and regulate tumor angiogenesis. Furthermore, deregulated expression of Id proteins has been observed in some human malignancies. Therefore we hypothesized that the Id-1 gene may play a role in papillary thyroid carcinogenesis. METHODS: Id-1 gene expression was characterized by Northern blot analysis and Id-1 immunohistochemistry in human thyroid tissue. Id-1 gene expression and regulation was evaluated in a human papillary thyroid cancer cell line, TPC-1, by Northern blot analysis. RESULTS: The Id-1 gene was significantly overexpressed in papillary thyroid cancer compared with normal thyroid tissue from the same patients (n = 18) by both Northern blot analysis and semiquantitative Id-1 immunohistochemistry (P <.001). Id-1 immunoreactivity was primarily localized to the cytoplasm of the thyroid follicular cells. In the TPC-1 cell line, stimulation by TSH and serum up-regulated Id-1 mRNA expression 1.5- and 4.0-fold, respectively. Activation of the mitogen intracellular protein kinase A and protein kinase C signaling pathways also up-regulated Id-1 mRNA expression. Inhibition of Id-1 mRNA expression with Id-1 antisense oligonucleotide inhibited growth compared with control Id-1 sense and random oligonucleotides (P <.05). CONCLUSIONS: The Id-1 gene is overexpressed in papillary thyroid cancer. Id-1 may play a role in the regulation of growth in papillary thyroid cancer.
Inhibitors of differentiation and DNA binding-1 (Id-1) have been demonstrated to oppose Ets-mediated activation of p16INK4a. As p16INK4a protein is inactivated in hepatocellular carcinoma (HCC), we aimed to investigate the role of Id-1 in regulating p16INK4a expression during the development of HCC in HCC patients and direct ectopic Id-1 introduction into the PLC/PRF/5 HCC cell line. Sixty-two HCC samples were recruited for evaluation of Id-1 and proliferating cell nuclear antigen (PCNA) protein expression. The messenger RNA (mRNA) expression of Id-1 and p16INK4a was detected by quantitative reverse transcription-polymerase chain reaction. For in vitro Id-1 transfection, five Id-1 transfected clones were isolated and the effect of ectopic Id-1 introduction was investigated by 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, flow cytometry, immunostaining and western blot. Our results showed that Id-1 was over-expressed in HCC specimens both at mRNA and protein levels. Over-expression of Id-1 protein was correlated with PCNA (r = 0.334, P = 0.033). HCC samples showing low Id-1 protein expression had a lower Id-1 mRNA level (340.2 versus 1467%, P = 0.039) and higher p16INK4a expression (195 versus -78.6%, P = 0.039) than samples with high Id-1 protein expression. In the PLC/PRF/5 HCC cell line study, ectopic Id-1 expression resulted in proliferation of HCC cells and an increased percentage of S phase cells and PCNA expression. The results showed that over-expression of Id-1 induces cell proliferation in HCC through inactivation of p16INK4a/retinoblastoma pathway. In conclusion, the results provided an insight for the understanding of the role of Id-1 in functional inactivation of p16INK4a in HCC.
The helix-loop-helix protein Id-1 inhibits the activity of basic helix-loop-helix transcription factors, and is an important regulator of cell growth and tissue-specific differentiation. We have shown (P. Y. Desprez et al., Mol. Cell. Biol., 18: 4577-4588, 1998) that ectopic expression of Id-1 inhibits differentiation and stimulates the proliferation and invasiveness of mouse mammary epithelial cells, and that there is a correlation between the levels of Id-1 protein and the aggressiveness of several human breast cancer cell lines. Here, we show that aggressive and metastatic breast cancer cells express high levels of Id-1 mRNA because of a loss of serum-dependent regulation that is mediated by a 2.2-kb region of the human Id-1 promoter. Three lines of evidence suggest that unregulated Id-1 expression may be an important regulator of the aggressive phenotype of a subset of human breast cancer cells: (a) a constitutively expressed Id-1 cDNA, when introduced into a nonaggressive breast cancer cell line (T47D), conferred a more aggressive phenotype, as measured by growth and invasiveness; (b) Id-1 was an important mediator of the effects of sex steroid hormones on T47D cell proliferation. Estrogen stimulated proliferation and induced Id-1 expression, whereas progesterone inhibited proliferation and repressed Id-1 expression. Progesterone repressed Id-1 expression, at least in part by repressing transcription. Most importantly, an antisense oligonucleotide that reduced Id-1 protein levels reduced the ability of estrogen to stimulate cell proliferation, whereas constitutive Id-1 expression rendered cells refractory to growth inhibition by progesterone; and (c) using a limited number of breast cancer biopsies, we showed that Id-1 was more frequently expressed in infiltrating carcinomas compared with ductal carcinomas in situ. Our results suggest that Id-1 can control the malignant progression of breast cancer cells, particularly that mediated by sex steroid hormones. Moreover, Id-1 has the potential to serve as a marker for aggressive breast tumors.
We investigated the pharmacokinetics of 11-hydroxyaclacinomycin X (ID-6105), a novel anthracycline, after intravenous (i.v.) bolus administration at a multiple dose every 24 h for 5 days in rats. To analyze ID-6105 levels in biological samples, we used an HPLC-based method which was validated in a pharmacokinetic study by suitable criteria. The concentrations of ID-6105 after the multiple administration for 5 days were not significantly different from the results after the single administration. The t1/2alpha, t1/2beta, Vdss, and CLt after the multiple administration were not significantly different from the values after the single administration. Moreover, the concentrations of ID-6105 1 min at day 1-5 after i.v. bolus multiple administration did not show the significant difference. Of the various tissues, ID-6105 mainly distributed to the kidney, lung, spleen, adrenal gland, and liver after i.v. bolus multiple administration. ID-6105 concentrations in the kidney or lung 2 h after i.v. bolus administration were comparable to the plasma concentration shortly after i.v. bolus administration. However, the ID-6105 concentrations in various tissues 48 h after i.v. bolus administration decreased to low levels. ID-6105 was excreted largely in the bile after i.v. bolus multiple administration at the dose of 3 mg/kg. The amounts of ID-6105 found in the bile by 12 h or in the urine by 48 h after the administration were calculated to be 14.1% or 4.55% of the initial dose, respectively, indicating that ID-6105 is mostly excreted in the bile. In conclusion, ID-6105 was rapidly cleared from the blood and transferred to tissues, suggesting that ID-6105 might not be accumulated in the blood following i.v. bolus multiple dosages of 3 mg/kg every 24 h for 5 days. By 48 h after i.v. bolus administration, ID-6105 concentrations in various tissues had decreased to very low levels. The majority of ID-6105 appears to be excreted in the bile.
BACKGROUND: The helix-loop-helix (HLH) proteins Id-1, Id-2 and Id-3 have been demonstrated to inhibit the activity of transcription factors and play an important role in regulating cell growth and tissue-specific differentiation. METHODS: To elucidate the involvement of Id in human oral squamous cell carcinoma (OSCC), we examined 83 surgical specimens and eight normal gingival mucosae for the expression of Id proteins by immunohistochemistry; in addition, some specimens of the OSCC and the normal gingivae were also examined for the expression of Id-1 mRNA by in situ hybridization (ISH), while Western blots were performed on six of the tumours and on cell lysates of five OSCC cell lines. We also explored the correlation between Id expressions and cellular proliferation indicating Ki-67 or clinical parameters. RESULTS: We discovered a higher and more frequent expression of Id-1 protein (27.7%) in human OSCC compared to that of Id-2 and Id-3 proteins (6.0 and 7.2%, respectively). Western blot analysis detected Id-1 protein in four of six tumour samples and in all cell lines. ISH demonstrated strong cytoplasmic localization of Id-1 mRNA in tumour samples at significantly higher levels compared to those of normal gingival mucosae. CONCLUSION: Id-1 protein expression significantly correlates with lymph node status, indicating that increased Id expression may relate to the metastatic behaviour in human OSCC.
The pineal gland is a major output of the endogenous vertebrate circadian clock, with melatonin serving as the output signal. In many species, elevated nocturnal melatonin production is associated with changes in pineal gene expression. In the current study, cDNA array analysis was used in an attempt to identify additional genes that exhibit day/night differential expression in the rat pineal gland. This revealed 38 candidate genes, including Id-1 (inhibitor of DNA binding and differentiation). Id-1 encodes a helix-loop-helix (HLH) protein that lacks a basic DNA binding domain and could affect pineal physiology via a dominant negative trans-acting regulatory activity. For this reason Id-1 was selected for further analysis. Id-1 was expressed in a major population of pineal cells and the Id-1 protein was associated with a nuclear complex. The levels of Id-1 mRNA and protein exhibit approximately six-fold day/night rhythms. In contrast, the related genes Id-2 and Id-3 do not exhibit marked day/night differences in pineal expression. Rhythmic Id-1 expression is primarily limited to a C-terminally extended splice variant of Id-1, which would restrict the functional output of the rhythm to protein binding partners of this isoform of Id-1. Our findings add to the body of evidence indicating that transcriptional regulators play a role in neuroendocrine rhythms, and extend this by introducing the concept of a dominant negative HLH involvement. The rhythm in Id-1 in the pineal gland provides an experimental opportunity to identify Id-1-binding partners which may also be involved in Id-1 activity in other functional contexts.
PURPOSE: The helix-loop-helix protein Id-1 serves to prevent basic helix-loop-helix transcription factors from binding to DNA, thus, inhibiting the transcription of differentiation associated genes. Over expression of Id-1 has been reported in certain tumors, such as breast, esophageal, pancreatic and medullary thyroid cancers. In Noble rats we have previously demonstrated that up-regulation of Id-1 is closely associated with the development of sex hormone induced prostate cancers. Therefore, we hypothesized that over expression of Id-1 would also occur in human prostate cancer and Id-1 protein may serve as a potential marker for prostate carcinogenesis. To test this hypothesis we analyzed Id-1 messenger RNA and protein expression by in situ hybridization and immunohistochemical study in human normal prostate, benign prostatic hyperplasia (BPH) and prostate cancer tissues. MATERIALS AND METHODS: Pathological specimens were obtained from 19 patients with BPH and 47 with prostate carcinoma, representing a complete range of Gleason grades. A total of 12 normal prostate tissue specimens were used for comparison. Immunohistochemical study was performed using the polyclonal antibody against human Id-1 protein and an RNA probe was generated from Id-1 complementary DNA for in situ hybridization. RESULTS: Negative to weak expression of Id-1 in normal prostate or BPH tissue was observed on immunohistochemical study and in situ hybridization. In contrast, all prostate cancer biopsies showed significant positive Id-1 expression in tumor cells at the messenger RNA and protein levels. Furthermore, Id-1 expression was stronger in poorly differentiated than in well differentiated carcinomas, suggesting that the level of Id-1 expression may be associated with tumor malignancy. CONCLUSIONS: Our results suggest that over expression of Id-1 may have important roles in the development of prostate cancer. The potential use of Id-1 protein as a marker for prostate cancer should be further explored.
The conditions neccessary for production of inhibitor of DNA synthesis (IDS) by rat lymphocytes were investigated. In concanavalin A (Con A)-stimulated lymph node cell (LNC) cultures, IDS production was not detected in the culture supernatant during the first 24 hr, and it increased gradually after that to reach a maximum at 3 to 4 days. When the cells were pretreated with mitomycin C, IDS was not produced, suggesting that DNA synthesis of LNC or a LNC subpopulation is necessary for IDS production. In contrast, Con A-stimulated spleen cells priduced a high level of IDS within 24 hr, and its production fell off sharply thereafter. Con A-stimulated rat thymocytes also produced IDS reaching a maximum at 2 to 3 dyas. However, thymus cells from rats treated with hydrocortisone 48 hr previously did not produce IDS. This finding implies that cortisol-sensitive (cortical) thymocytes are capable of producing IDS and cortisol-resistant (medullary) thymocytes are not. IDS production by lymphoblasts was proportional to cell number and unaffected eith by cell density (1 to 10 x 106/ml) or by the concomitant presence of normal cells from spleen, lymph node, or thymus. Thus Con A-stimulated cells, after becoming blasts, appear to produce IDS automatically wihtout affecting or being affected by other cells. Both spleen and thymus cells from rats injected with a large dose of antigen (ovalbumin, 100 mg, i.p.) 24 hr in advance produced substantial amounts of IDS in culture within 24 hr in the absence of mitogen or additional antigen, but not the cells from rats injected with an immunizing dose (1 mg) of the same antigen. The cells producing IDS in the spleen were shown to be adherent to glass wool, and those in the thymus were partially so. IDS production by antigen-stimulated spleen cells was abrogated by injecting rats with bromodexyuridine (BUdR) at 0 and 12 hr after the ovalbumin. These findings suggest that a subpopulation ofadherent spleen cells (possibly resembling cortical thymocytes), which begins to proliferate within a few hours after a large dose of systemic antigen, produces IDS. This may account for increased nonspecific suppressor activity observed at the same time.
OBJECTIVE: To study eluates of intravenous gamma globulin (IVGG) prepared from affinity columns of human cationic IgG myeloma proteins bearing anti-DNA idiotype (Id) markers 16/6, F4, 3I, and 8.12 for possible anti-Id (combining site) blocking activity. METHODS: Anti-DNA idiotypic antibody activity was studied in 3 preparations of IVGG containing high, medium, and low levels of IgG anti-F(ab')2, and in 4 other commercial IVGG preparations. Affinity-purified IgG anti-DNA (APAD) from systemic lupus erythematosus (SLE) patients was biotinylated, and binding to DNA coated on enzyme-linked immunosorbent assay plates was used to measure anti-DNA antibody activity. IVGG was adsorbed to Sepharose 4B affinity columns linked to a panel of cationic human IgG myeloma proteins positive for anti-DNA Id markers 16/6, F4, 3I, and 8.12. Material adsorbing to such columns was eluted at low pH (2.5) and after neutralization, tested for its ability to inhibit biotinylated APAD reacting with DNA. RESULTS: Only 0.05-0.9% of IVGGs bound firmly to Id affinity columns. These IVGGs were then eluted, using pH 2.5 glycine-saline and eluates neutralized to pH 7.4. Column flowthrough and eluate fractions were compared for their ability to block SLE APAD reacting with DNA. Significant inhibition of SLE APAD combining sites was observed with eluates from anti-DNA Id affinity columns; however, no correlation between IVGG anti-F(ab')2 activity and true anti-Id blocking of APAD was apparent. No residual anti-Id activity remained in column flowthrough fractions. No anti-Id blocking activity was recorded for IVGG eluates from human cationic myeloma columns devoid of the 4 anti-DNA Id markers. DNase treatment of IVGG or Id column eluates did not affect anti-Id blocking activity. Thus, all detectable anti-DNA idiotypic antibody capable of blocking SLE anti-DNA combining sites bound to Id+ affinity columns. Column eluates also showed some relative concentration of IgG anti-DNA activity, which was of lower affinity for DNA than antibodies also present in eluates which blocked anti-DNA combining sites. CONCLUSION: The presence of both anti-DNA and antiidiotypic (anti-combining site) activity in human anti-DNA Id column eluates indicates that epibodies from IVGG are relatively concentrated when this strategy is used. This approach may lead to a new strategy for treatment of SLE nephritis.
Id proteins are dominant negative members of the helix-loop-helix (HLH) transcription factor family which are involved in the differentation of many cell types, including glia. We have recently identified the adult rat pineal gland as a major site of Id-1 and Id-3 expression. In the present study, double fluorescence immunocytochemical analysis was used to examine the co-localization of Id-1 and Id-3 with both neuronal (synaptophysin, betaIII-tubulin) and astrocytic markers (GFAP, vimentin, S-100beta) in the rat pineal. In addition to localizing Id-1 and Id-3 protein to the melatonin-producing pinealocytes, we have also made the novel observation that Id-1, but not Id-3, is highly expressed in a population of vimentin-positive/S-100beta-positive/GFAP-negative astrocytes. Surprisingly, Id-1 was primarily cytoplasmic in these cells, and expression extended throughout the cellular processes. The pineal has been recognized previously as a unique region of the central nervous system in which a vimentin-positive/GFAP-negative glial phenotype is maintained in adult mammals. The exclusion of Id-1 from GFAP-positive cells, and expression in a population of vimentin-positive pineal astrocytes is evidence of a role for Id-1 in the adult stabilization of one form of astrocyte. These results identify the rat pineal gland as a model system for the functional analysis of Id-1.
It has been suggested that Id-1 has a critical role in the tumour progression and aggressiveness of several human cancers. However, the clinicopathological and biological significance of Id-1 overexpression remains unclear in human primary cancer. To investigate the association between Id-1 expression and cell proliferation or tumour angiogenesis, we examined the cell cycle kinetic indices (the proliferation and apoptotic indices, PI and AI) and intratumoral microvessel density (MVD) in 65 human pancreatic cancers. We also investigated the relationship between its expression and various clinicopathological factors to determine the clinical significance of Id-1 overexpression. Out of a total 65 cases, 32 (49.3%) showed overexpression of Id-1 vs normal tissues. Id-1 expression was found to be significantly associated with MVD (P=0.002). In further analysis of subgroups with higher and lower Id-1 expression, tumours with higher Id-1 expression (scores 4 and 5) showed significantly higher MVD than tumours with lower expression of Id-1 (scores 2 and 3) (111.18+/-57.14 vs 64.13+/-28.19, P<0.001). However, no significant association was found between Id-1 overexpression and patient survival rate. No significant association was also found between Id-1 expression and cell cycle kinetic indices (PI or AI) in pancreatic cancer. Moreover, the overexpression of Id-1 protein was not correlated with any significant clinicopathologic factors. These findings indicate that Id-1 overexpression is closely related with tumour angiogenesis and a higher density of intratumoral vessel, but that it is not associated with a poorer prognosis of survival or a higher cell proliferative potential in human pancreatic cancer.
Ids are dominant-negative helix-loop-helix (HLH) proteins that play overlapping yet distinct roles in antagonizing basic HLH transcription factors. Although Ids affect myogenesis, neurogenesis, and B-cell development, little is known about their in vivo functions in epithelia. We have examined the effects of forced expression of Id-1 in the small intestinal epithelium of adult chimeric mice. 129/Sv embryonic stem cells, transfected with DNA containing Id-1 under the control of transcriptional regulatory elements that function in all intestinal epithelial cell lineages, were introduced into C57Bl/6 (B6) blastocysts heterozygous for the ROSA26 marker. The B6 ROSA26/+ intestinal epithelium of the resulting adult chimeras produces Escherichia coli beta-galactosidase, allowing identification of this internal control cell population. Chimeras produced from nontransfected embryonic stem cells served as additional controls. Immunohistochemical studies of the control chimeras indicated that the small intestinal epithelium supports a complex pattern of endogenous Id expression. Id-1 is restricted to the cytoplasm; levels do not decrease as descendants of multipotent intestinal stem cells differentiate. Id-2 and Id-3 are only detectable in nuclei; levels increase markedly as epithelial cells differentiate. Forced expression of Id-1 in the 129/Sv epithelium results in a decline in Id-2 and Id-3 to below the limits of immunodetection. A subset of chimeric-transgenic mice lacked growth factor- and defensin-producing Paneth cells in their 129/Sv epithelium and also developed intestinal adenomas. These changes were not present in normal control chimeras. Adenomas were composed of proliferating beta-Gal-positive and -negative epithelial cells, suggesting that they arose through cooperative interactions between 129/Sv(Id-1) and B6 ROSA26/+ cells. These chimeras provide a model for studying how perturbations in Id expression affect tumorigenesis.
Increasingly, evidence supports the function of the helix-loop-helix protein Id-1 (inhibitor of differentiation/DNA binding-1) as an oncogene. Over-expression of Id-1 is not only observed in many types of human cancer but its expression levels have been correlated with cancer progression. However, little is known about the molecular mechanisms responsible for the function of Id-1. Recently, we and others reported that Id-1-induced cell proliferation was mediated through a Raf/MEK signalling pathway. In this study, we investigated if ectopic Id-1 expression in nasopharyngeal carcinoma cells had any protective effect on taxol-induced death, which is also regulated through Raf/MEK pathway. Using four stable Id-1 transfectant clones, we found that exogenous Id-1 expression led to phosphorylation of Raf-1 and MEK1/2 kinases, which was associated with resistance to taxol. Treatment of the Id-1 expressing cells with a MEK inhibitor, PD098059, resulted in an increased taxol-induced apoptosis rate in Id-1 transfectants compared with the vector control. In addition, the fact that the taxol-induced apoptosis rate, down-regulation of Bcl-2 and up-regulation of Bax were suppressed by PD098059 treatment in Id-1 expressing cells indicates that the Id-1 induced cellular protection against apoptosis is mediated through Raf/MEK signalling pathways. Our results suggest that Id-1 may be an upstream regulator of the Raf/MEK signalling pathway, which plays an essential role in protection against taxol-induced apoptosis. Our evidence also indicates a novel treatment strategy to increase anticancer drug-induced apoptosis through inactivation of the Id-1 protein.