Alterations of mismatch repair protein expression in benign melanocytic nevi, melanocytic dysplastic nevi, and cutaneous malignant melanomas.

Immunoperoxidase-staining methods were used to examine the expression of hMLH1, hMSH2, and hMSH6 mismatch repair (MMR) proteins in 50 melanocytic lesions. Microsatellite instability (MSI), screened previously in these lesions by polymerase chain reaction-based microsatellite assay, showed low-level microsatellite instability (MSI-L) in 11 of 22 melanocytic dysplastic nevi (MDN) and two of nine primary cutaneous malignant melanomas (CMMs) but not in the benign melanocytic nevi (BN). Mismatch repair proteins were widely expressed in the epidermis and adnexal structures. All lesions showed positive immunoreactivity with a gradual decrease in the MMR staining values during the progression from BN to MDN to CMMs. The average percentage of positively (PP) stained cells for hMLH1, hMSH2, and hMSH6 in BN was 85.50 +/- 1.95, 77.90 +/- 4.50, and 87.11 +/- 1.85, respectively. The PP cell values in CMMs were significantly reduced as compared with BN (75.22 +/- 3.57, p= 0.01; 56.11 +/- 8.73, p= 0.02; 65.22 +/- 6.47, p = 0.0002 for hMLH1, hMSH2, and hMSH6, respectively). No comparable significant difference was found between microsatellite stable and MSI-L lesions (p = 0.173, p = 0.458, and p = 0.385), suggesting a lack of correlation between MMR expression and MMR function. There was a direct correlation between PP cell values of hMSH2 and hMSH6 (R = 0.39, p = 0.008), implying that their expression could be regulated by a common mechanism. Thus, an important finding of these studies was the reduction of MMR protein levels in CMMs; whether this reflects underlying genetic or epigenetic mechanisms is still to be determined.

Comprehensive analysis of 112 melanocytic skin lesions demonstrates microsatellite instability in melanomas and dysplastic nevi, but not in benign nevi.

INTRODUCTION: the length of DNA repetitive sequences (microsatellite instability (MSI)) represent distinct tumorigenic pathways associated with several familial and sporadic tumors. MATERIAL AND METHODS: To investigate the prevalence and frequency of MSI in melanocytic lesions, the polymerase chain reaction (PCR)-based microsatellite assay was used to examine formalin-fixed, paraffin-embedded tissues of 30 benign melanocytic nevi, 60 melanocytic dysplastic nevi (MDN), and 22 primary vertical growth phase cutaneous malignant melanomas (CMM). Twenty-four microsatellite markers at the 1p, 2p, 3p, 4q and 9p chromosomal regions were used. RESULTS: MSI was found at 1p and 9p in MDN and CMM but not in benign melanocytic nevi. The overall prevalence of MSI was 17/60 (28%) in MDN and 7/22 (31%) in CMM. The frequency of MSI ranged from 2/24 (9%) to 4/24 (17%) and was most commonly found at D9S162. There was a statistically significant correlation between degree of atypia and frequency of MSI (p<0.001) in MDN. There were two MSI banding patterns: band shifts and additional bands. CONCLUSIONS: The data presented revealed the presence of low-frequency MSI (MSI-L) at the 1p and 9p regions in both MDN and CMM. Whether the MSI-L pattern reflects a defect in mismatch repair genes is still to be determined.

An early lesion in hepatic carcinogenesis: loss of heterozygosity in human cirrhotic livers and dysplastic nodules at the 1p36-p34 region.

Loss of heterozygosity (LOH) of chromosome 1 has been suggested, by karyotyping, to be an initial episode in human hepatocarcinogenesis. However, this alteration has not yet been investigated in cirrhotic nodules (CNs) or dysplastic nodules (DNs). In an initial study from explanted or resected cirrhotic livers, LOH in 1p36-p32 was examined in 31 hepatocellular carcinomas (HCCs), 25 low-grade dysplastic nodules (LGDNs), and 24 high-grade dysplastic nodules (HGDNs). In HCCs, LOH was detected most frequently at loci D1S2843 (1p36.1) (28.6%), D1S513 (1p34.3) (29.2%), and MYCL1 (1p34.1) (28.6%). In HGDN and LGDN, LOH incidences at D1S513 were 11.1% and 13.6%, respectively. To further refine those results and to determine sequential relationships among CN, DN, and HCC, LOH was next studied in an additional 53 HCCs, 56 HGDNs, 30 LGDNs, and 215 CNs from 11 explanted human cirrhotic livers, including 30 "nodule-in-nodule" lesions. Seven markers between D1S2843 (1p36.12) and MYCL1 (1p34.1), and 1 each at D1S484 (1q24.1), IGF2R-3 (6q26), and TP53 (17p13.1) were used. LOH at D1S2843 and D1S513 was detected in HCCs (20.4% and 23.5%, respectively), HGDNs (7.7% and 18.5%), LGDNs (13.6% and 6.9%), and CNs surrounding either HCCs or DNs (7.4% and 8.3%). These results demonstrate that LOH at D1S2843 and D1S513 are early events in human liver carcinogenesis. Data from CN surrounding either HCCs or DN, and also nodule-in-nodule lesions, provide evidence supporting a CN-->DN-->HCC progression. Different deletion patterns from multiple HCCs and DNs suggest independent origins for carcinogenesis in the same individual.

Effect of acute administration of N-nitrosopyrrolidine to male Syrian golden hamsters.

A protocol has been developed which decreases the time for administration of N-nitrosopyrrolidine (NPYR) to male Syrian golden hamsters from 25 weeks to a single i.p. injection. Animals were divided into five groups: group I received two 0.5-mmol doses on alternate days; group II was given three 0.33-mmol doses on alternate days; group III received a single dose of 0.5 mmol; group IV was given a single dose of 0.25 mmol and group V served as a control and received saline. Preneoplastic and neoplastic changes in the upper respiratory tract and liver were observed in all carcinogen-treated groups. The number of animals with laryngeal and tracheal tumors in the NPYR-treated groups was dose-dependent. Groups I and II, respectively, had 21 of 26 (81%) and 18 of 24 (75%) animals with either laryngeal or tracheal tumors. Groups III and IV showed 4 of 12 (33%) and 3 of 13 (23%) hamsters with these tumors. No laryngeal or tracheal tumors were observed in control animals. These results indicate that a single dose of NPYR is sufficient to induce respiratory tract tumors in Syrian golden hamsters.

Differential responses of two inbred rat strains to a choline-deficient diet during liver carcinogenesis.

We examined the effect of a choline-devoid (CD) diet on the development of gamma-glutamyltranspeptidase (GGT)-positive foci in both sexes of the inbred rat strains Fischer 344 and PVG/R8. Following partial hepatectomy, 7 to 8 week old animals were given a choline-supplemented diet for 1 week. Two groups were then formed: one remained on choline-supplemented diet as control, and the other was switched to the CD diet. The animals were killed 10, 16 and 24 weeks later. Liver samples were then stained with hematoxylin-eosin and Masson's trichromic, and histochemically analyzed for GGT. Fatty degeneration and collagen formation was severe in F344 males while it was mild or absent in F344 females and in both sexes of PVG rats. Stereochemical quantitation showed that F344 males had a significantly greater increase in the number of positive liver foci (as well as in their mean volume and the percentage of liver occupied by them) than F344 females and PVG animals of either sex (P < 0.01). These results suggest that not only sex but also the genotype of the host plays a role in the different responses to a CD diet. In depth analysis of these factors should prove valuable to investigate this dietary model of hepatocarcinogenesis further.