CUL5 is required for thalidomide-dependent inhibition of cellular proliferation.

Angiogenesis is essential for cancer metastasis, thus the discovery and characterization of molecules that inhibit this process is important. Thalidomide is a teratogenic drug which is known to inhibit angiogenesis and effectively inhibit cancer metastasis, yet the specific cellular targets for its effect are not well known. We discovered that CUL5 (previously identified as VACM-1), a scaffold protein in E3 ligase complexes, is involved in thalidomide-dependent inhibition of endothelial cell growth.

Nuclear localization signal sequence is required for VACM-1/CUL5-dependent regulation of cellular growth.

VACM-1/CUL5 is a member of the cullin family of proteins involved in the E3 ligase-dependent degradation of diverse proteins that regulate cellular proliferation. The ability of VACM-1/CUL5 to inhibit cellular growth is affected by its posttranslational modifications and its localization to the nucleus. Since the mechanism of VACM-1/CUL5 translocation to the nucleus is not clear, the goal of this project was to determine the role that the putative nuclear localization signal (NLS) we identified in the VACM-1/CUL5 (PKLKRQ) plays in the cellular localization of VACM-1/CUL5 and its effect on cellular growth.

New insights into the mechanism for VACM-1/cul5 expression in vascular tissue in vivo.

Vasopressin-activated calcium-mobilizing (VACM-1)/cul5 is the least conserved member of a cullin protein family involved in the formation of E3-specific ligase complexes that are responsible for delivering the ubiquitin protein to their target substrate proteins selected for ubiquitin-dependent degradation. This chapter summarizes work to date that has focused on VACM-1/cul5's tissue-specific expression in vivo and on its potential role in the control of specific cellular signaling pathways in those structures. As mammalian cells may contain hundreds of E3 ligases, identification VACM-1/cul5 as a specific subunit of the system that is expressed in the endothelium and in collecting tubules, structures known for their control of cellular permeability, may have significant implications when designing studies to elucidate the mechanism of water conservation.

Aquaporin-2 levels in vitro and in vivo are regulated by VACM-1, a cul 5 gene.

Background: In the renal collecting duct, vasopressin regulates water permeability by a process that involves stimulation of adenylyl cyclase activity, cAMP production and subsequent translocation of water channel aquaporin-2 (AQP2) into the apical plasma membrane. We have previously shown that in cos 1 cells in vitro, both adenylyl cyclase activity and cAMP production can be regulated by VACM-1, a cul 5 gene that forms complexes involved in protein ubiquitination and subsequent degradation.

Methods: To extend these observations further, the effects of changes in hydration state on the expression of VACM-1 at the mRNA and the protein level were examined in rats deprived of water (WD) for 24 hrs.

VACM-1/cul5 expression in vascular tissue in vivo is induced by water deprivation and its expression in vitro regulates aquaporin-1 concentrations.

VACM-1, a cul5 gene product, when overexpressed in vitro, has an antiproliferative effect. In vivo, VACM-1/cul5 is present in tissues involved in the regulation of water balance. Neither proteins targeted for VACM-1/cul5-specific degradation nor factors that may regulate its expression in those tissues have been studied.