Biomedical subjects

G Venta-Perez

Publications and source records attributed to G Venta-Perez.

4 recordsLinked to original sources

PubMed1997

Two cytodifferentiation agent-induced pathways, differentiation and apoptosis, are distinguished by the expression of human papillomavirus 16 E7 in human bladder carcinoma cells.

Many transformed cells have been found to lose the capacity to proliferate and undergo differentiation following exposure to hybrid polar agents. This study investigates the mechanism by which hexamethylene bisacetamide (HMBA) suppresses the proliferation of the human bladder carcinoma line, T24. We found that following a 24-h exposure to HMBA, T24 proliferation was inhibited, and cells arrested in G1 phase and underwent morphological maturation. HMBA-induced cessation of proliferation was mediated, in part, by effects on cell cycle regulatory proteins. In T24 cells cultured without HMBA, E2F complexes predominantly with p107. In culture with inducer, p107 protein decreased, pRB and p130 were converted to underphosphorylated forms, and E2F was shifted into complexes with pRB and p130. To determine whether the formation of pRB:E2F and p130:E2F complexes was required for the HMBA-induced G1 arrest, the ability of the pocket proteins to bind E2F was blocked by enforced expression of human papillomavirus 16 E7. Following culture with HMBA, the T24 clones expressing E7 died, whereas vector-alone T24 clones arrested in G1 phase. T24/E7-1 cells did not form pRB:E2F or p130:E2F complexes upon culture with HMBA; rather, E2F was present in its free form. T24/E7-1 cells cultured with HMBA initially accumulate in G1. By day 2, they have entered into S phase, and by day 3, over 80% of the cells became apoptotic. Taken together, these studies enlarge the repertoire of demonstrated developmental pathways that may be triggered in transformed cells, depending upon their molecular status, and may provide potential therapeutic opportunities for cancer.

Acetamides↗

PubMed1996

Changes in E2F DNA-binding activity during induced erythroid differentiation.

The cytodifferentiation agent hexamethylene bisacetamide (HMBA) is an inducer of differentiation of a variety of transformed cells, including the murine erythroleukemia (MEL) cell line. Induction of differentiation of MEL cells is a multistep process resulting in cessation of cell division and phenotypic maturation (including hemoglobin production). To investigate HMBA-induced MEL cell differentiation, we have analyzed the regulation of the E2F transcription factor. E2F regulates the transcription of several genes whose products are involved in both cell cycle regulation and differentiation. In nuclear extracts from uninduced MEL cells, three complexes were detected using gel mobility assays with the E2F/E2 oligonucleotide. The complex with the fastest mobility is the free form of E2F binding to DNA, and the more slowly migrating complexes contain E2F, p107, and cdk2. By 8 h of HMBA induction and for the remainder of the differentiation process, the free E2F complex is not detected, and only complexes of slower mobility, which contain p107 and cdk2, are found. The level of p107 protein increases during induction of differentiation; there is no change in the level of cdk2 protein and E2F-4 and DP-1 proteins during the first 4 days. The level of E2F-1 mRNA does not change, but a new form of E2F is detected during induction of differentiation. Thus, HMBA causes a selective loss in the free E2F DNA-binding complex, an increase in p107 protein, and an increase in a form of E2F protein during MEL cell differentiation.

Acetamides↗

PubMed1993

Hexamethylenebisacetamide-induced erythroleukemia cell differentiation involves modulation of events required for cell cycle progression through G1.

Hexamethylenebisacetamide (HMBA), a potent inducer of differentiation of transformed cells such as murine erythroleukemia cells, causes a prolongation of the G1 phase of the cell cycle during which commitment to terminal differentiation is first detected. Removal of HMBA prior to the G1 phase aborts commitment. To further define the relationship between the G1 phase and commitment to differentiation, we used two inhibitors of cell cycle progression: aphidicolin, which blocks cells at the G1/S interphase, and deferoxamine, which blocks cells at an earlier stage during G1. HMBA-induced prolongation of G1 is associated with the accumulation of underphosphorylated retinoblastoma protein, decrease in cyclin A protein levels, and commitment to differentiation. G1 arrest of murine erythroleukemia cells induced by aphidicolin or deferoxamine is not associated with accumulation of under-phosphorylated retinoblastoma protein, suppression of cyclin A protein, or commitment of cells to terminal differentiation. Neither of the cell cycle inhibitors alters the effect of HMBA in inducing the G1-associated changes or commitment to differentiation. Taken together, the present findings indicate that the site of action of HMBA which leads to commitment is in a stage of the G1 phase prior to the point of cell cycle block caused by deferoxamine or aphidicolin. HMBA appears to cause cell differentiation with suppression of cell cycle progression by an action that affects events required for cell progression through G1, including accumulation of underphosphorylated retinoblastoma protein and changes in regulation of cyclin levels.

Acetamides↗

PubMed1987

Expression of normal and mutant ras proteins in human acute leukemia.

The expression of normal and mutant ras genes in human acute leukemias was assessed by the direct analysis of p21ras polypeptides, using immunoprecipitation with monoclonal antibodies. High-resolution two-dimensional gel electrophoresis permits the identification of a wide array of activated ras alleles encoding proteins with single amino acid substitutions at any of several positions. The products of three ras genes, H-ras, N-ras, and K-ras, were detected in each of 33 specimens of fresh leukemic cells. The normal K-ras and N-ras polypeptides were substantially more abundant than H-ras p21 in all samples. In over three-fourths of the cases the total amount of p21ras exceeded that seen in control hematopoietic cell lines. The level of ras expression did not correlate simply with clinical parameters, although the two samples with the most abundant p21ras were obtained from patients with relapsed T-cell acute lymphocytic leukemia (ALL). Abnormal p21ras, consistent with oncogenic activation, was found in eight patients. Six of 11 samples from acute myelocytic leukemia (AML) patients displayed a mutant N-ras p21, while only one of 20 ALL specimens had abnormal N-ras, and one had a mutant H-ras. In every case the mutant protein comprised a minority of total p21ras. In two T-cell ALL cell lines both normal and activated N-ras gene products were expressed at equal levels. By contrast, in five fresh AML samples the abnormal N-ras protein was several-fold less abundant than the normal N-ras p21. This finding implies that only a proportion of leukemic cells in an individual patient may carry the mutant ras oncogene.

Acute Disease↗