Biomedical subjects

H L Hsu

Publications and source records attributed to H L Hsu.

26 records · Page 2Linked to original sources

PubMed1996

Dynamic changes of NuMA during the cell cycle and possible appearance of a truncated form of NuMA during apoptosis.

We have demonstrated that dynamic redistribution of nuclear-mitotic apparatus (NuMA) protein in the cell cycle is correlated temporally and spatially with its biochemical modifications. In interphase, NuMA behaves solely as a 220 kDa nuclear matrix-associated protein. After initiation of DNA condensation during mitosis, NuMA is phosphorylated by Cdc2 kinase into a 240 kDa form which is transported quickly to the centrosomal region. Once cells have passed the metaphase-anaphase transition, the 240 kDa form of NuMA either becomes a 180 kDa truncated form which is fated to be degraded completely before mitotic exit, or returns to the 220 kDa form that relocates to the daughter nuclei and remains throughout interphase. Apparently, a proteolytic enzyme is activated during the late stages of mitosis. After induction of a 180 kDa form of NuMA in interphase HeLa cells by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, nuclear apoptotic phenomena including chromatin condensation, DNA fragmentation, and micronucleation were observed. However, the same treatment did not induce apoptosis in mitotic phase-arrested HeLa cells. The 180 kDa form of NuMA was demonstrated to be a truncated product, at least lacking the tail domain. When HL60 cells were stimulated by diverse apoptosis inducers such as camptothecin, staurosporine, cycloheximide, and A23187, the extent of NuMA cleavage to produce a 180 kDa product was comparable with the degree of oligonucleosomal laddering. NuMA cleavage is likely to be a consequence of the onset of apoptosis. The intact 220 kDa NuMA functions in interphase cells to retain the nuclear structural integrity. Additionally, NuMA appears to act as a nuclear structural target for a death protease during apoptosis.

Antibodies, Monoclonal↗

PubMed1994

Positive and negative transcriptional control by the TAL1 helix-loop-helix protein.

Tumor-specific activation of the TAL1 gene is the most common genetic defect associated with T-cell acute lymphoblastic leukemia. The TAL1 gene products possess a basic helix-loop-helix (bHLH) motif, a protein-dimerization and DNA-binding domain found in several transcription factors. TAL1 polypeptides interact, in vitro and in vivo, with class A bHLH proteins (e.g., E47) to form heterodimers with sequence-specific DNA-binding activity. In this study, we show that TAL1 can regulate the transcription of an artificial reporter gene that contains binding sites for bHLH heterodimers involving TAL1. Transcription of the reporter is strongly induced by E47-E47 homodimers and moderately induced by TAL1-E47 heterodimers. Thus, in a cellular environment that allows formation of E47-E47 homodimers (e.g., in the absence of Id regulatory proteins) TAL1 can repress transcription by recruiting E47 into bHLH complexes with less transcriptional activity (i.e., TAL1-E47 heterodimers). However, in other settings TAL1 can activate transcription because TAL1-E47 heterodimers are more resistant to negative regulation by Id proteins. Hence, TAL1 can potentially regulate transcription in either a positive or negative fashion.

Animals↗

PubMed1994

Formation of in vivo complexes between the TAL1 and E2A polypeptides of leukemic T cells.

Tumor-specific activation of the TAL1 gene occurs in approximately 25% of patients with T-cell acute lymphoblastic leukemia (T-ALL). The TAL1 gene products possess a basic helix-loop-helix (bHLH) domain that interacts in vitro with the bHLH proteins (E12 and E47) encoded by the E2A locus. We have now applied two independent methods, the two-hybrid procedure and co-immunoprecipitation analysis, to demonstrate that TAL1 and E2A polypeptides also associate in vivo. These studies show that the bHLH domain of TAL1 selectively interacts with the bHLH domains of E12 and E47, but not with the Id1 helix-loop-helix protein. TAL1 does not self-associate to form homodimeric complexes, implying that the in vivo functions of TAL1 depend on heterologous interaction with other bHLH proteins such as E12 and E47. Co-immunoprecipitation analysis revealed the presence of endogenous TAL1/E2A complexes in Jurkat cells, a leukemic line derived from a T-ALL patient. Thus, the malignant properties of TAL1 may be due to obligate interaction with the E2A polypeptides.

Base Sequence↗

PubMed1994

Preferred sequences for DNA recognition by the TAL1 helix-loop-helix proteins.

Tumor-specific activation of the TAL1 gene is the most common genetic alteration seen in patients with T-cell acute lymphoblastic leukemia. The TAL1 gene products contain the basic helix-loop-helix (bHLH) domain, a protein dimerization and DNA-binding motif common to several known transcription factors. A binding-site selection procedure has now been used to evaluate the DNA recognition properties of TAL1. These studies demonstrate that TAL1 polypeptides do not have intrinsic DNA-binding activity, presumably because of their inability to form bHLH homodimers. However, TAL1 readily interacts with any of the known class A bHLH proteins (E12, E47, E2-2, and HEB) to form heterodimers that bind DNA in a sequence-specific manner. The TAL1 heterodimers preferentially recognize a subset of E-box elements (CANNTG) that can be represented by the consensus sequence AACAGATGGT. This consensus is composed of half-sites for recognition by the participating class A bHLH polypeptide (AACAG) and the TAL1 polypeptide (ATGGT). TAL1 heterodimers with DNA-binding activity are readily detected in nuclear extracts of Jurkat, a leukemic cell line derived from a patient with T-cell acute lymphoblastic leukemia. Hence, TAL1 is likely to bind and regulate the transcription of a unique subset of subordinate target genes, some of which may mediate the malignant function of TAL1 during T-cell leukemogenesis.

Amino Acid Sequence↗

PubMed1994

The MAP kinase phosphorylation site of TAL1 occurs within a transcriptional activation domain.

Alteration of the TAL1 gene is the most common genetic lesion found in patients with T cell acute lymphoblastic leukemia. TAL1 encodes a basic helix-loop-helix transcription factor that is phosphorylated on serine residue 122 by the mitogen-activated protein (MAP) kinase ERK1. Here we show that the amino-terminal sequences of TAL1 (residues 1-166) function in vivo as a transcriptional activation domain. Mutation of serine residue 122 reduces the potency of the transactivation domain by more than half. The data suggest that the amino-terminal transactivation domain of TAL1 is positively regulated by S122 phosphorylation and that the functional properties of TAL1 can be influenced by signal transduction pathways that involve the MAP kinases.

Animals↗

PubMed1993

Products of the TAL1 oncogene: basic helix-loop-helix proteins phosphorylated at serine residues.

TAL1 gene rearrangement is observed in nearly 30% of patients with T-cell acute lymphoblastic leukemia (T-ALL), and thus it represents the most common genetic lesion associated with this disease. Nevertheless, the presence of TAL1 gene products in normal or leukemic cells has not been reported. Therefore, immunoprecipitation with anti-TAL1 antisera was used to demonstrate the presence of TAL1 phosphoproteins, pp42TAL1 and pp22TAL1, in both T-ALL and erythroleukemia cell lines. The pp42TAL1 and pp22TAL1 proteins appear to be phosphorylated forms of full-length and truncated TAL1 gene products respectively. Phosphoamino acid analysis revealed that pp42TAL1 contains phosphoserine residues. The TAL1 phosphoproteins were detected in all of the T-ALL cell lines that harbor obvious TAL1 gene rearrangements. Interestingly, pp42TAL1 and pp22TAL1 were also present in some, but not all, of the T-ALL lines without detectable TAL1 gene alterations. Therefore, TAL1 activation may promote leukemogenesis in a far greater proportion of T-ALL patients than the 30% that bear gross TAL1 gene rearrangements.

Basic Helix-Loop-Helix Proteins↗

PubMed1991

Enhancer-binding activity of the tal-1 oncoprotein in association with the E47/E12 helix-loop-helix proteins.

Almost 30% of patients with T-cell acute lymphoblastic leukemia (T-ALL) bear structural alterations of tal-1, a presumptive proto-oncogene that encodes sequences homologous to the helix-loop-helix (HLH) DNA-binding and dimerization domain. Analysis of the tal-1 gene product reveals that its HLH domain mediates protein-protein interactions with either of the ubiquitously expressed HLH proteins E47 and E12. The resultant tal-1/E47 and tal-1/E12 heterodimers specifically recognize the E-box DNA sequence motif found in eucaryotic transcriptional enhancers. Hence, the tal-1 protein shares biochemical properties with other tissue-specific HLH proteins that control cell type determination during myogenesis (e.g., MyoD1) and neurogenesis (e.g., achaete-scute). The data suggest that HLH heterodimers involving tal-1 may function in vivo as transcriptional regulatory factors that influence cell type determination during hematopoietic development.

Base Sequence↗

PubMedDate not supplied

Steroids used to desensitize penicillamine allergy in Wilson disease.

Patients with Wilson disease require life-long treatment and penicillamine is the drug of choice. We present a 14-year-old boy with Wilson disease who developed hypersensitivity reaction 2 days after starting penicillamine therapy. His symptoms included fever, maculopapular rash and lip edema. The allergic reaction disappeared when penicillamine was discontinued, but relapsed after reinstituting penicillamine at a lower dose. Desensitization was attempted by introducing steroid therapy, the dose of 0.7 mg per kilogram per day of prednisolone for 2 days, then penicillamine was successfully tolerated. Subsequent tapering of the daily prednisolone dose was performed till it was discontinued one month after treatment began. We suggest that concomitant use of steroid and penicillamine should be used for the treatment of patients who develop penicillamine intolerance.

Adolescent↗