Biomedical subjects

P O Humbert

Publications and source records attributed to P O Humbert.

4 recordsLinked to original sources

PubMed2006

The tumour-suppressor Scribble dictates cell polarity during directed epithelial migration: regulation of Rho GTPase recruitment to the leading edge.

Altered expression of human Scribble is associated with invasive epithelial cancers, however, its role in tumour development remains unclear. Mutations in Drosophila Scribble result in loss of polarity, overproliferation and 3D-tumourous overgrowth of epithelial cells. Using complementation studies in Drosophila we recently demonstrated that expression of human Scribble can also regulate polarity and restrict tissue overgrowth. Here, we have undertaken a detailed study of human Scribble function in the polarized mammary cell line, MCF10A. We show that although Scribble does not seem to be required for apical-basal polarity or proliferation control in MCF10A cells, Scribble is essential for the control of polarity associated with directed epithelial cell migration. Scribble-depleted MCF10A cells show defective in vitro wound closure and chemotactic movement. The cells at the wound edge fail to polarize, show reduced lamellipodia formation and impaired recruitment of Cdc42 and Rac1 to the leading edge. Furthermore, we show that this function is relevant in vivo as Scribble mutant mice show defective epidermal wound healing. This data identifies an essential role for mammalian Scribble in the regulation of the polarity specifically involved in directed epithelial migration.

Breast Neoplasms↗

PubMed2000

E2f3 is critical for normal cellular proliferation.

E2F is a family of transcription factors that regulate both cellular proliferation and differentiation. To establish the role of E2F3 in vivo, we generated an E2f3 mutant mouse strain. E2F3-deficient mice arise at one-quarter of the expected frequency, demonstrating that E2F3 is important for normal development. To determine the molecular consequences of E2F3 deficiency, we analyzed the properties of embryonic fibroblasts derived from E2f3 mutant mice. Mutation of E2f3 dramatically impairs the mitogen-induced, transcriptional activation of numerous E2F-responsive genes. We have been able to identify a number of genes, including B-myb, cyclin A, cdc2, cdc6, and DHFR, whose expression is dependent on the presence of E2F3 but not E2F1. We further show that a critical threshold level of one or more of the E2F3-regulated genes determines the timing of the G(1)/S transition, the rate of DNA synthesis, and thereby the rate of cellular proliferation. Finally, we show that E2F3 is not required for cellular immortalization but is rate limiting for the proliferation of the resulting tumor cell lines. We conclude that E2F3 is critical for the transcriptional activation of genes that control the rate of proliferation of both primary and tumor cells.

Animals↗

PubMed2000

E2F4 is essential for normal erythrocyte maturation and neonatal viability.

The retinoblastoma protein (pRB) plays a key role in the control of normal development and proliferation through the regulation of the E2F transcription factors. We generated a mutant mouse model to assess the in vivo role of the predominant E2F family member, E2F4. Remarkably, loss of E2F4 had no detectable effect on either cell cycle arrest or proliferation. However, E2F4 was essential for normal development. E2f4-/- mice died of an increased susceptibility to opportunistic infections that appeared to result from craniofacial defects. They also displayed a variety of erythroid abnormalities that arose from a cell autonomous defect in late stage maturation. This suggests that E2F4 makes a major contribution to the control of erythrocyte development by the pRB tumor suppressor.

Animals↗

PubMed1997

oct-2 gene disruption eliminates the peritoneal B-1 lymphocyte lineage and attenuates B-2 cell maturation and function.

Targeted mutation of the gene for the Oct-2 transcription factor in mice caused neonatal lethality and abrogated mitogen-induced proliferation and differentiation of mature B lymphocytes in vitro. Here we show that Oct-2 is required for normal humoral responses upon immunization with T cell-dependent as well as T-independent Ags. oct-2-null T cell behavior was normal, implying a B cell-restricted lesion. oct-2-/- B cells displayed aberrant behavior during activation in vitro: both acquisition of markers of cellular activation and cell survival were diminished. Production of early B lineage cells in the bone marrow was normal, yet mature B cells were under-represented in blood and lymphoid organs. Furthermore, peritoneal B-1 lymphocytes were not detected in animals with a reconstituted oct-2-/- lymphoid system. We conclude that Oct-2 is required for B-1 cell maintenance and for normal Ag-driven maturation of conventional B cells in vivo.

Animals↗