Decreased expression of the growth hormone receptor and growth hormone binding protein in rat liver nodules

Effects of recombinant human growth hormone on growth of human gastric carcinoma xenograft model in nude mice

AIM: To study effects of recombinant human growth hormone (rhGH) on growth of a human gastric carcinoma cell in vivo.

METHODS: Experimental mice were divided into control group, rhGH group, oxaliplatin (L-OHP) group and rhGH+L-OHP group. Cultured human gastric carcinoma cells BGC823 were inoculated into right axilla of nude mice and carcinoma xenograft model was established successfully. Inhibitory rate of xenograft tumor growth was estimated by measuring tumor volume; expression of proliferating cell nuclear antigen (PCNA), Bax and Bcl-2 proteins of xenograft tumor was detected using immunohistochemical S-P method.

RESULTS: Tumor growth inhibitory rate, the positive expression rate of PCNA, Bax and Bcl-2 were 49.3%, 58.2%, 65.2% and 59.2% in rhGH+L-OHP group respectively; 46.6%, 62.5%, 59.7% and 64.7% in L-OHP group; 5.0%, 82.7%, 23.2% and 82.2% in rhGH group and 0, 77.8%, 23.5% and 80.3% in control group. There was significant difference between rhGH+L-OHP group (or L-OHP group ) and control group or rhGH group (P < 0.05), whereas there were no significant differences (P > 0.05) between L-OHP group and rhGH+L-OHP group and between rhGH group and control group.

CONCLUSION: rhGH does not accelerate the proli-feration of human gastric cancer cell in vivo.

In vitro effects of recombinant human growth hormone on growth of human gastric cancer cell line BGC823 cells

AIM: To study the effects of recombinant human growth hormone (rhGH) on growth of human gastric cancer cell line in vitro.

METHODS: Experiment was divided into control group, rhGH group, oxaliplatin (L-OHP) group and rhGH+L-OHP group. Cell inhibitory rate, cell cycle, cell proliferation index (PI) and DNA inhibitory rate of human gastric cancer line BGC823, at different concentrations of rhGH treatment were studied by cell culture, MTT assay and flow cytometry.

RESULTS: The distinctly accelerated effects of rhGH on multiplication of BGC823 cell line were not found in vitro. There was no statistical significance between rhGH group and control group, or between rhGH+L-OHP group and L-OHP group (P > 0.05). The cell growth curve did not rise. Cell inhibitory rate and cells arrested in G₀-G₁ phase were obviously increased. Meanwhile, cells in S phase and PI were distinctly decreased and DNA inhibitory rate was obviously increased in rhGH+L-OHP group in comparison with control group and rhGH group, respectively (P < 0.01). Cell inhibitory rate showed an increasing trend and PI showed a decreasing trend in rhGH+L-OHP group compared with L-OHP group.

CONCLUSION: In vitro rhGH does not accelerate the multiplication of human gastric cancer cells. It may increase the therapeutic efficacy when it is used in combination with anticancer drugs.

Differentially expressed transcripts in neoplastic hepatic nodules and neonatal rat liver studied by cDNA microarray analysis

The molecular mechanisms underlying hepatocarcinogenesis remain unclear. Wistar rats treated with 2-AAF develop hepatocarcinoma in histologically well-characterised stages. In our study, cDNA microarrays were used to measure the expression of 3,000 genes during the progression of liver carcinogenesis in persistent neoplastic nodules. Because tumours frequently revert into a more poorly differentiated phenotype, we also studied the expression of the same set of transcripts in neonatal rat liver. Approximately 2,000 transcripts gave a detectable signal in experiments comparing gene expression in nodules and control tissue. Approximately 8% of these were identified as differentially expressed in liver nodules. The differentially expressed genes fell into several categories with putative or demonstrated roles in signal transduction, metabolism, detoxification, cell-structure and transport. Many of the differentially expressed genes in nodules were not previously known to be regulated during liver carcinogenesis. A universal transcript profile for gene expression in hepatic liver nodules and neonatal liver has been created.

Overexpressed growth hormone (GH) synergistically promotes carcinogen-initiated liver tumour growth by promoting cellular proliferation in emerging hepatocellular neoplasms in female and male GH-transgenic mice

BACKGROUND/AIMS

Growth hormone (GH), when overexpressed in male and female GH-transgenic mice, is known to induce liver tumours within 1 year. This study aimed to gain a clearer understanding of the interaction between GH and tumour cells in vivo.

METHODS/RESULTS

The carcinogen diethylnitrosomine (DEN) was administered to neo-natal transgenic and non-transgenic mice maintained in a "hepatocarcinogenesis resistant" genetic background (C57BL/6J). Macroscopic, microscopic and liver weight/body weight ratio analyses revealed that carcinogen-induced hepatocarcinogenesis was dramatically accelerated in young GH-transgenic mice compared to non-transgenic counterparts. Image analysis of microscopic hepatocellular neoplasms showed rapidly increasing tumour burdens, and neoplastic foci size over time in young adult GH-transgenic mice. The magnitude of enhanced tumour growth was equivalent in both male and female transgenic mice, whereas much lower and sexually dimorphic tumour growth rates (males>females) were observed in non-transgenic mice treated with DEN. BrdU labelling experiments demonstrated that rapid tumour growth in carcinogen-treated GH-transgenic mice was due to the promotion of cell proliferation in emerging lesions. Tumour cell proliferation in young GH-transgenic mice was 2.6- and 4-fold higher, respectively, than that observed in similar age male and female non-transgenic mice. Interestingly, both GH-transgenic and non-transgenic mice displayed progressively slower tumour growth rates in older animals.

CONCLUSION

Overall, GH synergistically promotes carcinogen-induced hepatocarcinogenesis in both sexes of GH-transgenic mice by stimulating tumour cell proliferation.

Membrane biochemistry and chemical hepatocarcinogenesis

Biochemical membrane alterations appearing during the process of chemical carcinogenesis are described. Emphasis is put on membrane composition, structure, and biogenesis. In this presentation the knowledge gained from experimental studies of liver and skin in the process of cancer development is acknowledged. Important biochemical changes have been reported in lipid composition, fatty acid saturation, constitutional enzyme expression, receptor turnover and oligomerization. Functional consequences of the altered membrane structure is discussed within the concepts of regulation of cell proliferation, regulation of membrane receptor expression, redox control, signal transduction, drug metabolism, and multidrug resistance. Data from malignant tumours and normal tissue are addressed to evaluate the importance of the alterations for the process and for the eventual malignant transformation.

Role of growth hormone in the regulation of the c-myc gene during progression of sex-differentiated rat liver carcinogenesis in the resistant hepatocyte model

In this study, we extended the previous observations of a growth hormone-regulated sex difference in hepatic c-myc expression in the resistant hepatocyte model during the selection/promotion phase, when sex differences in growth rate of enzyme-altered foci are first identified, to studies of the regulation of this gene during later stages of hepatocarcinogenesis. The expression of the c-myc gene was studied in preneoplastic nodules, hepatocellular carcinomas, and the corresponding surrounding livers of male and female Wistar rats treated according to the resistant hepatocyte model. In males, nodules isolated 8 and 11-12 mo after initiation and hepatocellular carcinomas exhibited a 2.5- to threefold higher c-myc expression than the surrounding liver. In females, no increase in c-myc expression was observed in nodules 8 mo after initiation, while nodules isolated after 11-14 mo and tumors showed a twofold and threefold increase, respectively, when compared with the surrounding tissue. Increased transcription of the c-myc gene was observed in nuclei from male nodules isolated 11 mo after initiation compared with nuclei from the surrounding liver. The difference in transcription between male nodules and surrounding tissue is similar for the first and second exon of the gene. Continuous infusion of growth hormone to nodule-bearing male rats 8 and 11 mo after initiation decreased c-myc expression in the surrounding tissue and downregulated the expression in 8-mo nodules to the level in the surrounding liver. No significant decrease in response to growth hormone treatment was seen in 11-mo nodules. In hypophysectomized nodule-bearing males, nodular c-myc remained upregulated. Taken together, the data showed that the sex difference in c-myc expression was maintained during a large part of the progression period. Furthermore, the loss of growth hormone regulation of the c-myc gene in advanced male nodules indicated an escape from normal regulatory mechanisms during progression. These findings might reflect a role for the c-myc gene in sex-differentiated rat liver carcinogenesis.