Biomedical subjects

G Prem Veer Reddy

Publications and source records attributed to G Prem Veer Reddy.

6 recordsLinked to original sources

PubMed2006

Regulatory processes affecting androgen receptor expression, stability, and function: potential targets to treat hormone-refractory prostate cancer.

Prostate cancer cells rely on androgen receptor (AR) for proliferation and survival. Therefore, curing prostate cancer will require elimination of AR. Although androgen is the natural ligand that activates AR, AR activity is also subject to regulation by growth factor/growth factor receptor-stimulated signaling pathways that control the cell cycle. Cell cycle regulatory proteins and protein kinases in signaling pathways affected by growth factors can lead to AR activation in the absence of androgen. While downstream signaling proteins such as cyclins, cyclin-dependent kinases (CDKs), and pRB can modulate AR activity, upstream signaling pathways involving protein kinases such as mitogen-activated protein kinases, protein kinase A, and protein kinase B/Akt can affect post-translational modification of AR to affect not only AR function but also AR stability. Calcium and calmodulin (CaM), essential for proliferation and viability of a number of cells, including prostate cancer cells, play an important role in AR expression, stability, and function. CaM affects AR partly by interacting directly with AR and partly by activating protein kinases such as Akt and DNA-PK that can phosphorylate AR. The ubiquitin/26S proteasome pathway responsible for timely destruction of cell cycle regulatory proteins whose levels impede cell cycle progression also induces AR expression by activating NF-kappaB, and promotes AR activity by participating in the assembly of an AR transcription complex. Maspin, a serine protease inhibitor that is known mostly for its role as a tumor suppressor can also regulate AR intracellular localization and function by competing with AR for binding to the chaperone protein Hsp90 and co-repressor HDAC1, respectively. This perspective reviews the experimental evidence implicating these diverse cellular processes in AR expression, stability, and/or function, and presents a rationale for disrupting these cellular processes as a viable option for the treatment of both the hormone-sensitive and the hormone-insensitive prostate cancer.

Calcium↗

PubMed2005

Effect of GGC (glycine) repeat length polymorphism in the human androgen receptor on androgen action.

BACKGROUND: The human androgen receptor (AR) contains glutamine (CAG) and glycine (GGC) repeat length polymorphisms. Normal glutamine repeat length affects androgen action, but an effect of normal glycine repeat length has not been studied. METHODS: To determine whether glycine/GGC repeat length affects AR function, we constructed AR cDNA expression vectors with different GGC repeat lengths in the physiological range (13-17 GGCs). AR constructs were transfected into AR-negative DU145 human prostate cancer cells along with an androgen-responsive reporter plasmid (PSA-firefly luciferase) and a transfection efficiency control plasmid (Renilla luciferase). RESULTS: Glycine repeat length had no significant effect on androgen-dependent AR transactivation activity expressed as firefly luciferase per unit amount of AR protein. However, AR protein levels (normalized for transfection efficiency) were inversely affected by glycine repeat length (P < 0.001; r = -0.9; e.g., GGC13 yielded 2.7 times more AR protein than did GGC17). Therefore, the net amount of AR activity per cell would be higher in cells expressing AR with a short glycine repeat. Based on programs that predict structure from RNA sequence, the GGC repeat can form a hairpin structure, the free energy of which decreases (i.e., hairpin stability increases) as a function of increasing repeat length. This suggests that hairpin stability may interfere with translation, accounting for the inverse effect of GGC repeat length on AR protein yields. CONCLUSIONS: The ability of a short GGC repeat to enhance androgen action provides a biologically plausible mechanism to account for reports that a short GGC repeat in the AR gene is a risk factor for prostate cancer.

Androgens↗

PubMed2004

Regulation in S phase by E2F.

The DNA synthetic S phase of the unperturbed cell cycle is a closed system, as compared to regulation of G(1) by external growth factors. The E2F family provides internal control in S phase by transcribing genes required for deoxynucleotide triphosphate (dNTP) and DNA synthesis. Furthermore, over expression of E2F-1 activates programmed cell death (apoptosis), a safeguarding signal of aberrant growth of cells that have become carcinogenic. Mechanisms for control of E2F-1 are thus essential. The hypothesis is proposed that deoxythymidine triphosphate (dTTP) allosterically feedback controls E2F-1 to regulate both DNA synthesis and apoptosis. This may act either upon production of E2F-1 or its degradation.

Allosteric Regulation↗

PubMed2004

Effect of a short CAG (glutamine) repeat on human androgen receptor function.

BACKGROUND: The human androgen receptor (AR) gene contains an uninterrupted CAG repeat that is polymorphic in length in the general population (range, 11-31 CAG's; median, 21). The CAG repeat encodes a glutamine repeat in the N-terminal transactivation domain of the AR protein. We previously reported that a 17-CAG AR gene was much more common in a cohort of men with prostate cancer (8.5%) than in the general European American population (1.3%). This suggested that a 17-CAG repeat may have pathophysiological consequences. The goal of the present study was to directly test the hypothesis that a 17-CAG repeat might uniquely affect androgen action in human prostate cancer cells. METHODS: DU145 cells, lacking endogenous AR, were transiently transfected with an AR expression plasmid (with a CAG repeat ranging in length from 14 to 25) and an androgen-responsive reporter plasmid (PSA-luciferase). RESULTS: We found a significant effect of CAG repeat length on AR protein levels per unit amount of DNA transfected (one-way ANOVA, P = 0.02), indicating the need to express transactivation data per unit amount of AR protein. CAG17 AR had 40% more transactivation activity per unit amount of AR protein than CAG21 AR (P < 0.01). CONCLUSIONS: Thus, an AR with a 17-CAG repeat may mediate more efficacious growth stimulation of androgen-dependent prostate epithelial cells, and thereby increase the risk that prostate cancer cells develop more efficiently into a clinically significant cancer.

Blotting, Western↗

PubMed2002

Resveratrol induces prostate cancer cell entry into s phase and inhibits DNA synthesis.

Resveratrol has an apoptotic effect on a variety of cancer cells. Changes in cell cycle regulatory processes contributing to the antiproliferative effect of resveratrol remain largely unknown. Our studies revealed that, in androgen-sensitive LNCaP cells, the effect of resveratrol on DNA synthesis varied dramatically depending on the concentration and the duration of treatment. In 1-h-treated cells, resveratrol showed only an inhibitory effect on DNA synthesis, which increased with increasing concentration (IC50 = 20 microM). However, when treatment duration was extended to 24 h, we observed a dual effect of resveratrol on DNA synthesis. At 5 to 10 microM it caused a 2- to 3-fold increase in DNA synthesis, and at > or =15 microM, it inhibited DNA synthesis. The increase in DNA synthesis was seen only in LNCaP cells, but not in androgen-independent DU145 prostate cancer cells or in NIH3T3 fibroblast cells. The resveratrol-induced increase in DNA synthesis was associated with enrichment of LNCaP cells in S phase, and a concurrent decrease in nuclear p21Cipl and p27Kip1 levels. Furthermore, consistent with the entry of LNCaP cells into S phase, there was a dramatic increase in nuclear Cdk2 activity associated with both cyclin A and cyclin E. Taken together, our observations indicate that LNCaP cells, treated with resveratrol, are induced to enter into S phase, but subsequent progression through S phase is limited by the inhibitory effect of resveratrol on DNA synthesis, particularly at concentrations above 15 microM. Therefore, this unique ability of resveratrol to exert opposing effects on two important processes in cell cycle progression, induction of S phase and inhibition of DNA synthesis, may be responsible for its apoptotic and antiproliferative effects.

Androgens↗

PubMed2002

Cytokine receptor repertoire and cytokine responsiveness of Ho(dull)/Rh(dull) stem cells with differing potentials for G1/S phase progression.

OBJECTIVE: Subsetting of Hoechst 33342 dull (Ho(dull)) hematopoietic stem cells on the basis of rhodamine 123 (Rh) efflux utilizing an improved dual-dye efflux strategy resolves Ho(dull)/Rh(dull) stem cell subsets that differ with regard to their rate of recruitment and progression through the cell cycle upon exposure to cytokines. MATERIALS AND METHODS: Murine bone marrow cells were isolated by negative immunomagnetic selection using lineage-directed antibodies followed by Ho and Rh staining using a dual-dye efflux method. RESULTS: Ho(dull)/Rh(dull) stem cells that efflux Rh more efficiently (R1) exhibit a 4- to 8-hour delay in progression to S phase when stimulated by interleukin-3 (IL-3), IL-6, IL-11, and stem cell factor (SCF) compared to Ho(dull)/Rh(medium) stem cells, which retain low levels of Rh (R2). R1 and R2 cells show a hierarchical entry into S phase upon exposure to any or all of these cytokines. The R1 subset contains proportionately more high proliferative potential colony-forming cells than the R2 subset, but equivalent levels of engraftable stem cells at 3 and 8 weeks after competitive transplantation. Both R1 and R2 cells express c-kit, IL-3R, and IL-11R, whereas IL-6R and c-fms are only expressed by R1 or R2 cells, respectively. Cytokine stimulation of R1 and R2 cells induced cell cycle progression with elevated or induced expression of c-kit, c-fms, IL-2R, and IL-6R. CONCLUSION: These studies indicate that primitive marrow stem cells can be further subsetted by degree of Rh staining to reveal important functional phenotypic differences between cells with different levels of Rh staining.

Animals↗