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Biomedical subjects

J R Biggs

Publications and source records attributed to J R Biggs.

8 recordsLinked to original sources
PubMed1998

Activation of the mitogen-activated protein kinase pathway in U937 leukemic cells induces phosphorylation of the amino terminus of the TATA-binding protein.

Phorbol ester treatment of U937 leukemic cells results in the activation of numerous protein kinase pathways, followed by cell cycle arrest and differentiation into macrophage-like cells. Because major changes in gene transcription are associated with this process, the role of general transcription factors in the cell response to phorbol esters was examined. Experiments demonstrate that phorbol ester treatment of U937 cells stimulates the phosphorylation of the TATA-binding protein (TBP); this phosphorylation occurs within 30 min and is still apparent, although greatly reduced, at 4 h. The following results demonstrate that TBP phosphorylation occurs as a result of activation of an extracellular signal-regulated kinase (ERK) protein kinase: (a) overexpression of mitogen-activated protein kinase phosphatase-1 blocks phorbol 12-myristate 13-acetate (PMA)-induced phosphorylation of TBP both in vitro and in vivo; (b) pretreatment with the ERK kinase kinase inhibitor PD098059 also blocks PMA-induced phosphorylation of TBP both in vitro and in vivo; and (c) phosphorylation of TBP is observed when serum-starved NIH 3T3 cells are stimulated with fresh serum, another activator of the ERK pathway. TBP can be phosphorylated in vitro by extracts of U937 cells or by bacterially expressed activated ERK2; the phosphorylation sites were mapped to ERK kinase consensus sites in the TBP amino-terminal domain. Using glutathione S-transferase-TBP fusion proteins, cellular proteins that bind specifically to the TBP amino terminus have been identified. These observations suggest that ERK-mediated phosphorylation of TBP occurs during the PMA-induced differentiation of U937 cells and the stimulation of the G0-G1 transition in fibroblasts and could play a role in the regulation of TBP protein interactions and thus regulate gene transcription during these two processes.

3T3 Cells↗
PubMed1996

The role of the transcription factor Sp1 in regulating the expression of the WAF1/CIP1 gene in U937 leukemic cells.

The Waf1/Cip1 protein induces cell cycle arrest through inhibition of the activity of cyclin-dependent kinases and proliferating cell nuclear antigen. Expression of the WAF1/CIP1 gene is induced in a p53-dependent manner in response to DNA damage but can also be induced in the absence of p53 by agents such as growth factors, phorbol esters, and okadaic acid. WAF1/CIP1 expression in U937 human leukemic cells is induced by both phorbol ester, a protein kinase C activator, and by okaidaic acid, an inhibitor of phosphatases 1 and 2A. Both of these agents induce the differentiation of these leukemic cells toward macrophages. We demonstrate that phorbol esters and okadaic acid stimulate transcription from the WAF1/CIP1 promoter in U937 cells. This transcription is mediated by a region of the promoter between -154 and +16, which contains two binding sites for the transcription factor Sp1. Deletion or mutation of these Sp1 sites reduces WAF1/CIP1 promoter response to phorbol ester and okadaic acid, while a reporter gene under the control of a promoter containing only multiple Sp1 binding sites and a TATA box is induced by phorbol ester and okadaic acid. The WAF1/CIP1 promoter is also highly induced by exogenous Sp1 in the Sp1-deficient Drosophila Schnieder SL 2 cell line. These results suggest that phorbol ester and okadaic acid activate transcription of the WAF1/CIP1 promoter through a complex of proteins that includes Sp1 and basal transcription factors.

Base Sequence↗
PubMed1995

Repression of the Id2 (inhibitor of differentiation) gene promoter during exit from the cell cycle.

The Id2 gene is one of several "Id-like" genes which encode helix-loop-helix proteins which dimerize with basic helix-loop-helix proteins and inhibit binding to the DNA enhancer element known as an E box. By repressing the DNA binding activity of basic helix-loop-helix proteins, Id proteins inhibit transcription of tissue-specific genes in myoblasts, hematopoietic precursor cells, and other types of undifferentiated cells. Serum starvation results in the disappearance of Id gene transcripts in most types of cultured cells, and often induces differentiation of these cells. In order to gain some insight into this process, we have analyzed Id2 promoter function in the glioma cell line U87Y. We have isolated 300 base pairs of Id2 promoter sequence which is sufficient to repress the activity of a reporter gene in serum-starved U87Y cells, but induces the activity of the reporter gene when the cells are stimulated with fresh serum. Two regions within this 300 base pair sequence contain repressor elements; deletion of either region results in increased promoter activity. Both repressor regions serve as binding sites for a protein present in extracts from serum-starved U87Y cells but not in serum-stimulated cells.

Amino Acid Sequence↗
PubMed1995

Inhibitors of cyclin-dependent kinase and cancer.

Recent research has yielded a dramatic increase in the number of connections between oncogenesis and the proteins which regulate the cell cycle. Three classes of protein which inhibit the activity of cyclin-dependent kinases (CDKs) have emerged as potential targets for oncogenic inactivation. p16 and related proteins inhibit the cyclin/CDK complexes which regulate the transition from G1 to S phase; numerous studies have revealed that p16 is mutated in most tumor cell lines and in some types of primary tumor. p21/WAF1/Cip 1 and the related p27Kip protein inhibit a broader range of cyclin/CDK complexes than p16. Although the absence of p21/WAF1/Cip1 from cyclin/CDK complexes is correlated with cellular transformation, no mutations in this gene have been found in tumors or tumor-derived cell lines. A third class of genes which are potential targets for oncogenic inactivation are the kinases and phosphatases which regulate the activity of cyclin/CDK complexes by phosphorylation and dephosphorylation of the CDK proteins. Disruption of any of these genes would result in loss of normal regulation of cell growth.

Animals↗
PubMed1989

Reduced Nm23/Awd protein in tumour metastasis and aberrant Drosophila development.

Tumour metastasis is the principal cause of death for cancer patients. We have identified the nm23 gene, for which RNA levels are reduced in tumour cells of high metastatic potential. In this report we identify the cytoplasmic and nuclear Nm23 protein, and show that it also is differentially expressed in metastatic tumour cells. We also find that the human Nm23 protein has sequence homology over the entire translated region with a recently described developmentally regulated protein in Drosophila, encoded by the abnormal wing discs (awd) gene. Mutations in awd cause abnormal tissue morphology and necrosis and widespread aberrant differentiation in Drosophila, analogous to changes in malignant progression. The metastatic state may therefore be determined by the loss of genes such as nm23/awd which normally regulate development.

Amino Acid Sequence↗