Synergistic induction of anchorage-independent growth of NIH3T3 mouse fibroblasts by cysteine proteinase inhibitors and a tumor promoter

Drug-sensitivity pattern analysis for study of functional relationship between gene products

We have developed a method that we call 'drug-sensitivity pattern analysis', or DSPA, for analysis of protein function. Cells are transfected with cDNA of the test molecule, followed by analysis of the sensitivity of the transfected cells to multiple growth-inhibitory drugs. If two cDNA products have similar functions, their transfected cells should show similar drug-sensitivity patterns. The cDNAs of some signaling molecules were transfected into NIH3T3 or Ha-ras-transformed NIH3T3 (ras-NIH) cells and stable transfectants, which expressed high amounts of the gene product, were isolated. Chemosensitivity of the transfected clone was compared with the parental cells by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide method using more than 40 drugs. The chemosensitivity changes caused by the transfected gene were calculated and expressed numerically as 'drug chemosensitivity index' (DCI). When the DCI values were analyzed by regression analysis, a significant positive relationship between IkappaBalpha superrepressor and dominant-negative IKKbeta and an inverse relationship between p53 and Mdm2 were consistent with previous reports. Thus, the DSPA method is useful for identifying functional similarities between gene products.

Facilitation of adenoviral wild-type p53-induced apoptotic cell death by overexpression of p33(ING1) in T.Tn human esophageal carcinoma cells

To investigate the effect of p33(ING1) on wild-type p53 gene therapy, T.Tn human esophageal carcinoma cells were stably transfected with p33(ING1) cDNA. Infection with Ad-p53 (recombinant adenovirus containing wild-type p53) into p33-transfected cells reduced cell viability, while infection with empty vector had little effect. This reduced viability was shown to be due to apoptotic cell death by the TUNEL (terminal deoxynucleotidyl transferase-mediated nick end-labeling) assay. Following infection with Ad-p53, levels of p53 were similar in p33-expressing cells and in the parental line. However, levels of p21 and Mdm2 were elevated in p33-transfected cells. Nonetheless, this enhanced expression of Mdm2 appeared to be ineffective in downregulating p53. Transient transfection with mutant Mdm2 prior to Ad-p53 infection provided a significant protection as compared with cells transfected with wild-type Mdm2. These results imply a synergistic effect between p33 and p53 in the induction of apoptosis of human esophageal carcinoma cells. A role for Mdm2 in this synergism is suggested.

Regulation of transformed state by calpastatin via PKCepsilon in NIH3T3 mouse fibroblasts

Ca(2+)-activated neutral protease calpain is ubiquitously expressed and may have pleiotropic biological functions. We have previously reported that repeated treatment of NIH3T3 mouse fibroblasts with the calpain inhibitor N-acetyl-Leu-Leu-norleucinal (ALLN) resulted in the induction of transformed foci [T. Hiwasa, T. Sawada, and S. Sakiyama (1990) Carcinogenesis 11, 75-80]. To elucidate further the effects of calpain in malignant transformation of NIH3T3 cells, calpastatin, an endogenous specific inhibitor of calpain, was expressed in NIH3T3 cells by transfection with cDNA. G418-selected calpastatin-expressing clones showed a significant increase in the anchorage-independent growth ability. A similar increase in cloning efficiency in soft agar medium was also observed in calpain small-subunit-transfected clones. On the other hand, reduced expression of calpastatin achieved by transfection with calpastatin antisense cDNA in Ha-ras-transformed NIH3T3 (ras-NIH) cells caused morphological reversion as well as a decrease in anchorage-independent growth. When NIH3T3 cells were treated with ALLN for 3 days, cell growth was stimulated by approximately 10%. This growth stimulation by ALLN was not observed in ras-NIH cells, but recovered by expression of a dominant negative form of protein kinase C (PKC)epsilon but not by that of PKCalpha. Western blotting analysis showed that an increase in PKCepsilon was much more prominent than that of PKCalpha in NIH3T3 cells after treatment with ALLN. These results are concordant with the notion that calpain suppresses malignant transformation by predominant degradation of PKCepsilon.

Suppression of transformed phenotypes of Ha-ras-transformed NIH3T3 cells by caspase-2

Biological effects of caspases-1, -2 and -3 have been investigated by transfection of these human cDNAs into activated c-Ha-ras-transformed NIH3T3 mouse fibroblasts. High expression of caspase-2 but not caspase-1 or -3 induced flat revertant cells which lost the ability of anchorage-independent growth. Notably, these revertants contained a reduced amount of Ras protein. These suggest that caspase-2 exhibited a tumor-suppressive activity by affecting the expression level of Ras protein.