Cell adhesion to substratum and activation of tyrosine kinases are essentially required for G1/S phase transition in BALB/c 3T3 fibroblasts

AbstractCell adhesion to substratum and activation of tyrosine kinases are essential for the progression of cell cycle through G1 phase in mammalian cells. The kinetic studies of mouse BALB/c 3T3 fibroblasts showed that serum was no longer required for the progression of G1/S phase transition. In contrast, cell adhesion was essentially required in late GI phase, especially at the period of G1/S transition. Among the kinase inhibitors used to elucidate the signal transduction caused by cell adhesion, tyrosine kinase inhibitors, genistein and herbimycin A, blocked the G1/S transition most effectively when cells were exposed to the inhibitors at the period of GI/S transition. Cell adhesion was not critically required for cells to undergo DNA synthesis once they had passed the G1/S boundary, and the effects of tyrosine kinase inhibitors on the progression of S phase were also not critical. The expressions of histone H2B and dihydrofolate reductase (DHFR) genes (S phase specific genes) and also the transcription factor E2F-1 gene (an activator of DHFR gene) were suppressed when cells were cultured without adhesion or exposed to the tyrosine kinase inhibitors. These results suggest that cell adhesion to substratum plays an important role in the G1/S phase transition of mouse BALB/c 3T3 fibroblasts through the activation of tyrosine kinases other than growth factor receptor-tyrosine kinases

A1F-B, a novel CCAAT-binding transcription activator that interacts with the aldolase B promoter

AbstractWe describe here a 70 kDa transcription factor A1F-B, which preferentially binds to an element encompassing a CCAAT motif on the rat aldolase B promoter. Comparison of binding specificities, relative molecular masses, and subunit compositions with those of other known CCAAT-binding factors indicated that A1F-B is a novel member of CCAAT-binding factors

Immunological quantitation of tyrosinase from wild-type and albino mutant mice

AbstractThe relationship between gene dosage, enzyme activity, and level of immunologically cross-reacting material (CRM) was examined in mammalian tyrosinase (EC 1.14.18.1) by rocket immunoelectrophoresis. Skin extracts from mice heterozygous (C/c) and homozygous (c/c) for the albino locus contain 46% and 0% of CRM, respectively, as compared with wild-type (C/C) animals. Enzyme activity and CRM level were directly proportional in these genotypes, suggesting that the albino locus controls the quantity of tyrosinase produced in melanocytes

HISTOLOGICAL LOCALIZATION OF 4-S-CYSTEINYLPHENOL IN MELANOMA-BEARING MICE

4-S-cysteinylphenol (4-S-CP), the S-homologue of tyrosine, has been recently synthesized as a selective chemotherapeutic agent against malignant melanoma and has been shown to be a specific substrate for tyrosinase in vitro In vivo incorporation of 4-S CP into the B16 and Harding Passey (HP) melanomas and the systemic organs have been evaluated by the autoradiographic method .The distribution of the silver grains indicated that 4-S CP was selectively incorporated into both the B16 and HP melanomas. 4-S-CP was excreted mainly from the kidneys and there was an accumulation of 4-S-CP in the reticulo-endothelial system. These results seemed to contribute to the utilization of 4-S-CP and other related compounds as chemotherapeutic agents against malignant melanoma