Ethnic Differences of the p53 Genetic Alteration in Cutaneous Malignant Melanoma

BACKGROUND: There are significant differences in the clincopathologic pattern including the incidence, favor site, and histopathologic type between cutaneous malignant melanomas arising from whites, asians and blacks. These differences might suggest that there is a racial difference in the molecular tumorigenesis mechanism of malignant melanoma. METHODS: To determine the ethnic differences in tumorigenesis of malignant melanoma, we performed loss of heterozygosity (LOH) and sequencing analyses of the p53 gene in cutaneous malignant melanomas arising from 22 white American, 30 Korean and 15 black African patients. RESULTS: The frequency of LOH of the p53 gene is only 12.5% in white American patients, but the frequency is significantly higher in Korean (42.1%) and black African (61.5%) patients. We also detected 17 mutations (nonsense: 1, missense: 16) of the p53 gene in the cutaneous malignant melanomas of Koreans and black Africans, but none in those of white Americans: among the 16 missense mutations, 10 mutations were C:G to T:A transitional mutations. Of these, we also detected one GG (CC) to AA (TT) tandem mutation at the pyrimidine sequence. CONCLUSION: These results strongly suggest that there might be a racial difference in molecular carcinogenesis mechanisms among the cutaneous malignant melanomas occurring in white American, Korean and black African patients. But the role of the p53 genetic alteration in the genesis of melanomas in Korean and black African patients is subject to further evaluation.

Identification of Differentially Expressed Genes Using RNA Fingerprinting in Cell after DNA Damage

RNA fingerprinting using on arbitrary primed polymerase chain reaction (RAP-PCR) was carried out to identify differentially expressed genes in HL-60 cell after treatment of methylmethane sulfonate (MMS). Twenty differentially expressed PCR products were cloned and analyzed. We have successfully obtained eight partial cDNA sequences by TA cloning method. Among these, six cDNAs were up-regulated and two cDNAs were down-regulated after the MMS treatment. Of these six up-regulated cDNAs, 3 cDNAs were equivalent to known genes in the GenBank/EMBL databases with 98~100% homology searched by BLAST program: genomic DNA fragment containing CpGg island (clone 26h8), Human Rev interacting protein-1 (RIP-1), and human zinc finger protein-4 (HZF4). The sequences of the three remaining cDNA were entirely new genes, but we didn't try to identify a full cDNA sequence. Two clones called KIAA0060 and KIAA0065, were down-regulated in HL-60 cells after the MMS treatment. These findings suggest that the RNA fingerprinting method using RAP-PCR is an effective method which can identify and separate the differentially expressed cDNAs and that the isolated cDNAs might involve in regulation mechanism of apoptosis and/or cell cycle delay, especially a p53-independent pathway, in the cells after DNA damage. But the nature of cDNAs that we have isolated remains to be elucidated.

The Role of gadd and p53 Genes in Apoptosis and Cell Cycle Delay by Genotoxic Agents

The aim of this study was to investigate the relationships between the gadd genes expression and an apoptosis induction in two different growing cell types after treatments with cisplatin and methylmethan sulfonate (MMS). We have examined the kinetics and specificity of gadd45 and gadd153 expression following cisplatin and MMS treatments to HL-60 cells and primary cultured human kidney (HKN) cells. We have also determined an induction time of apoptosis by DNA fragmentation analysis and the presence of the cell cycle arrest by a flow cytometric measurement. The results were as follows. In non-adherent HL-60 cells, a typical ladder pattern was observed within 4 hours after treatments of 20 micrometer of cisplatin and 100 microgram/ml of MMS. At the same time while adherent HKN cells failed to exhibit a ladder pattern at even higher doses of genotoxic agents. Since HL-60 cells do not have p53 gene, these findings suggest the presence of a p53-independent apoptotic pathway. The increasing patterns of the mRNA levels of gadd45 and gadd153 varied with the type of genotoxic agents. In the case of MMS treatment, the induction was rapid and transient, regardless of the cell types. The mRNA level peaked at 4 hours after MMS treatment and markedly decreased after 12 hours. On the other hand, cisplatin-induced transcriptions of gadd45 and gadd153 continued to increase for at least 24 hours and reached a peak level at 48 hours after cisplatin treatment, regardless of the cell types. HL-60 cells revealed G2 arrest following 24 hours after cisplatin and MMS treatments. These findings suggest that the regulation mechanism of apoptosis between adherent and non-adherent cells, might be different and that gadd45 and gadd153 might have an important role in DNA repair rather than apoptosis. Also, the findings suggest that an expression pattern of gadd45 and gadd153 might be different according to the type of genotoxic agents.

Identification of Zinc Finger Genes that are Differentially Expressed upon Apoptosis of Ramos B Cells

Typical programmed cell death requires de novo macromolecular synthesis and shares common morphological changes referred to as apoptosis. To elucidate the molecular mechanism of apoptosis, we isolated 13 cDNA clones of zinc finger genes that are differentially expressed in calcium ionophore-induced apoptosis of Ramos human B cell by 'targeted RNA fingerprinting' protocol (Stone & Wharton, 1993). According to DNA sequence analysis of the 13 cDNA clones, three clones are identical with ZNF7, ZNF143 and MTB-Zf, respectively, and 8 out of the other 10 clones showed partial homology to known zinc finger genes. Differential expression was confirmed in the three known zinc finger genes by ribonuclease protection assay. ZNF7 and ZNF143 are up-regulated after induction of apoptosis, and, in contrast, MTB-Zf is down-regulated. According to the previous reports on these three genes, all of the three genes have been suspected to be tumor suppressor genes, but their functions have not been identified yet. Taken together, our results suggest that many of the novel and known zinc finger genes might play important roles in regulation of apoptosis and that these findings also provide clues as to the functions of the three putative tumor suppressor genes, ZNF7, ZNF143 and MTB-Zf in terms of apoptosis. In addition, the isolation of zinc finger genes by targeted RNA fingerprinting could be a straightforward approach for the identification of novel candidate genes associated with apoptosis.