Role of actin-regulatory gelsolin in control of cell growth

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1. We cloned a mutant gelsolin cDNA His321 from the flat revertant R1 of human activated Ha-ras oncogene-transformed NIH3T3 fibroblasts (EJ-NIH3TS). His321 suppressed tumorigenicity of EJ-NIH3T3. We expressed the His321 and wild-type gelsolin in Escherichia coli, purified them, and analyzed their effects on actin, polyphosphoinositol lipids and phospholipase C.His321 decreased actin-filament-severing activity and increased nucleating activity compared with wild-type gelsolin in vitro. Furthermore, compared to wild-type gelsolin both nucleation and severing by His321 were inhibited more strongly by the phosphoinositol lipids phosphatidylinositol 4-phosphate (PtdInsP) and phosphatidylinositol 4,5-bisphosphate (PtdInsP2). In addition, His321 inhibited PtdInsP2 hydrolysis by phospholipase C gamma 1 more strongly than wild-type gelsolin in vitro because of its higher binding capacity for phosphoinositol Lipid. Our results suggest that the segment G3 of gelsolin which contains the mutation i … More s functionally relevant for regulation of gelsolin's activities and that the region around the residue 321 may contain a phosphoinositol-lipid-binding site. Altered functions of His321 gelsolin might be important for the loss of tumorigenicity of the ras-transformed cells.2. We examined the expression of gelsolin in a number of human bladder and colon cancer cell lines and tissues. In all 6 bladder and 6 of 7 colon cancer cell lines and in 14 of the 18 bladder(77.8%)and 9 of 18 colon(50%)tumor tissues, gelsolin expression was undetectable or extremely low in comparison with its expression in normal bladder or colon epithelial cells. Furthermore, upon the introduction of the exogenous human or mouse authentic gelsolin cDNA into a human bladder cancer cell line UMUC-2 or a human colon cancer cell line LoVo, gelsolin transfectants of UMUC-2 and LoVo greatly reduced the colony-forming ability and the tumorigenicity in vivo. These results suggest that gelsolin plays a key role as a tumor suppressor in human urinary bladder and colon carcinogenesis. Less