Three-dimensional matrix suppresses E2F-controlled gene expression in glomerular mesangial cells

Abstract

Extracellular matrix (ECM) regulates mitogenesis of glomerular mesangial cells. Currently, however, the molecular mechanisms that mediate the control of cell growth by ECM are not fully elucidated. The effects of structurally distinct forms of type I collagen matrix on mesangial cell proliferation and cell cycle distribution were examined. Expressions of the cell cycle-regulatory transcription factor E2F and retinoblastoma susceptibility gene family proteins were also investigated. Mesangial cells cultured on monomeric collagen matrix showed a substantial growth response to serum. In contrast, mesangial cells cultured on polymerized collagen matrix exhibited arrest of the cell cycle in the G0/G1 phase. The induction of the quiescent phenotype was correlated with down-regulation of E2F-1, the prototypal transcription factor that controls cell cycle progression. The suppression of E2F-1 was associated with (1) dephosphorylation of retinoblastoma susceptibility gene proteins, pRB and p130, and (2) accumulation of E2F-pRB and E2F-p130 DNA binding complexes that bind to the E2F consensus sequence located in the E2F-1 promoter. Other E2F regulatory genes, including c-myc, cyclin A, and cdc 2, were also down-regulated in mesangial cells cultured on polymerized collagen matrix. These results suggest that a three-dimensional collagen induces cell cycle arrest via suppression of E2F-controlled gene expression in mesangial cells. Dephosphorylation of pRB and p130 and subsequent generation of transrepressor complexes, E2F-pRB and E2F-p130, may be involved in this process.