HIC-5: A Mobile Molecular Scaffold Regulating the Anchorage Dependence of Cell Growth

HIC-5 is a multidomain LIM protein homologous to paxillin that serves as a molecular scaffold at focal adhesions and in the nucleus. It forms mobile molecular units with LIM-only proteins, PINCH, and CRP2 and translocates in and out of the nucleus via a nuclear export signal (NES). Of note, NES of HIC-5 is distinctive in its sensitivity to the cellular redox state. Recently, the mobile units of HIC-5 have been suggested to be involved in the regulation of the anchorage dependence of cell growth. On loss of adhesion, an increase in reactive oxygen species in the cells modifies NES and stops shuttling, which leads to cell-cycle control. More specifically, the system circumvents nuclear localization of cyclin D1 and transactivates p21Cip1 in detached cells, thereby avoiding anchorage-independent cell growth. Thus, the HIC-5-LIM only protein complex has emerged as a fail-safe system for regulating the anchorage dependence of cell growth

Isolation of a novel ras-recision gene that is induced by hydrogen peroxide from a mouse osteoblastic cell line, MC3T3-E1

AbstractHydrogen peroxide appears to mediate growth factor actions, and it inhibits DNA synthesis in normal mouse osteoblastic cells (MC3T3-E1) at non-toxic doses. However the sensitivity of cells to H2O2 is greatly decreased in their ras-transformants. To understand the molecular basis of this sensitivity to H2O2, we attempted to identify H2O2-inducible cDNA clones from MC3T3 cells by differential screening of cDNA libraries, and one of such genes, named HIC-53, was isolated. The level of HIC-53 mRNA was moderately increased by H2O2 as well as by calcium ionophore or dexamethasone, but was not increased by the addition of serum, tumor promotimg phorbol ester, or epidermal growth factor. Among mouse organs, HIC-53 mRNA levels were higher in the kidney and lung, but were almost undetectable in the brain, heart, bone, muscle or spleen. In MC3T3 cells transformed with v-Ki-ras, the HIC-53 mRNA level was markedly decreased, and effect of H2O2 was abolished. Although the biological function of HIC-53 is unknown at present, the predicted amino acid sequence exhibited some similarity with bovine cardiac Na+/Ca+ exchanger. The nucleotide sequence of HIC-53 cDNA showed no significant similarity with other known gene sequences

Competitive Nuclear Export of Cyclin D1 and Hic-5 Regulates Anchorage Dependence of Cell Growth and Survival

Anchorage dependence of cell growth and survival is a critical trait that distinguishes nontransformed cells from transformed cells. We demonstrate that anchorage dependence is determined by anchorage-dependent nuclear retention of cyclin D1, which is regulated by the focal adhesion protein, Hic-5, whose CRM1-dependent nuclear export counteracts that of cyclin D1. An adaptor protein, PINCH, interacts with cyclin D1 and Hic-5 and potentially serves as an interface for the competition between cyclin D1 and Hic-5 for CRM1. In nonadherent cells, the nuclear export of Hic-5, which is redox-sensitive, was interrupted due to elevated production of reactive oxygen species, and cyclin D1 was exported from the nucleus. When an Hic-5 mutant that was continuously exported in a reactive oxygen species-insensitive manner was introduced into the cells, cyclin D1 was retained in the nucleus under nonadherent conditions, and a significant population of cells escaped from growth arrest or apoptosis. Interestingly, activated ras achieved predominant cyclin D1 nuclear localization and thus, growth in nonadherent cells. We report a failsafe system for anchorage dependence of cell growth and survival