Rapid induction of skin tumors in human but not mouse c-Ha-ras proto-oncogene transgenic mice by chemical carcinogenesis

Fate and plasticity of the epidermis in response to congenital activation of BRAF

Determining the developmental consequences of activated RAS and its downstream effectors is critical to understanding several congenital conditions caused by either germline or somatic mutations of the RAS pathway. Here we demonstrate that embryonic activation of BRAF in mouse ectoderm triggers both craniofacial and skin defects, including hyperproliferation, loss of spinous and granular keratinocyte differentiation, and cleft palate. RNA-sequencing reveals that despite an apparent block in spinous and granular differentiation, the epidermis continues to mature, expressing >80% of EDC genes and forming a hydrophobic barrier, both characteristic of later stages in epidermal development. Spinous and granular differentiation can be restored by pharmacologic inhibition of MEK or BRAF; however, in tissue recombination studies, phenotypic reversion was found to be non-cell autonomous and required dermal tissue to be present. These studies indicate that early activation of the RAF signaling pathway in the ectoderm has specific effects on progressive differentiation of the epidermis, which may be amendable to treatment using existing pharmacologic inhibitors.

New susceptibility locus for obesity and dyslipidaemia on chromosome 3q22.3

BACKGROUND

The muscle Ras (MRAS) gene resides on chromosome 3q22.3 and encodes a member of the membrane-associated Ras small GTPase proteins, which function as signal transducers in multiple processes including cell growth and differentiation. Its role in cardiovascular disease is not fully understood yet. In a preliminary study in heterozygous familial hypercholesterolaemia, we identified a locus linking the early onset of coronary artery disease (CAD) to chromosome 3q.22 and elected to sequence the MRAS gene using the MegaBACE DNA analysis system. In the present study, we investigated the association of seven single-nucleotide polymorphisms (SNPs) at this locus with CAD and its dyslipidaemia-related risk traits in 4,650 Saudi angiographed individuals using TaqMan assays by the Applied Biosystems real-time Prism 7900HT Sequence Detection System.

RESULTS

Among the studied SNPs, rs6782181 (p = 0.017) and rs9818870T (p = 0.009) were associated with CAD following adjustment for sex, age and other confounding risk factors. The rs6782181_GG also conferred risk for obesity (1,764 cases vs. 2,586 controls) [1.16(1.03-1.30); p = 0.017], hypercholesterolaemia (1,686 vs. 2,744) [1.23(1.02-1.47); p = 0.019], hypertriglyceridaemia (1,155 vs. 3,496) [1.29(1.01-1.45); p = 0.043] and low high-density lipoprotein-cholesterol (lHDL-chol) levels (1,935 vs. 2,401) [1.15(1.02-1.30); p = 0.023] after adjustment. Additionally, rs253662_(CT+TT) [1.16(1.01-1.32); p = 0.030] was associated with lHDL-chol levels. Interestingly, rs253662 (p = 0.014) and rs6782181 (p = 0.019) were protective against acquiring high low-density lipoprotein-cholesterol (hLDL-chol) levels (p = 0.014), while rs1720819 showed similar effects against CAD (p < 0.0001). More importantly, a 7-mer haplotype, ACCTGAC (χ2 = 7.66; p = 0.0056), constructed from the studied SNPs, its 6-mer derivative CCTGAC (χ2 = 6.90; p = 0.0086) and several other shorter derivatives conferred risk for obesity. hLDL-chol was weakly linked to CTAA (χ2 = 3.79; p = 0.052) and CCT (χ2 = 4.32; p = 0.038), while several other haplotypes were protective against both obesity and hLDL-chol level.

CONCLUSION

Our results demonstrate that the genomic locus for the MRAS gene confers risk for CAD, obesity and dyslipidaemia and point to the possible involvement of other genes or regulatory elements at this locus, rather than changes in the M-Ras protein function, in these events.

Tumor Promotion by 12-O-Tetradecanoylphorbol-13-Acetate in an Ultra-Short-Term Skin Carcinogenesis Bioassay Using rasH2 Mice

Assessment of the skin tumor–promoting potential of 12- O-tetradecanoylphorbol-13-acetate (TPA) after initiation with 7,12-dimethylbenz[ a]anthracene (DMBA) was conducted using rasH2 transgenic (Tg) mice and their nontransgenic (non-Tg) littermates. Mice were treated with DMBA (50 μg/100 μL acetone) on clipped back skin at the commencement of the study, and 1 week thereafter, TPA was applied at 8 μg/200 μL or 4 μg/200 μL acetone, once or twice weekly, for 7 weeks. Skin nodules were observed in the rasH2 Tg mice from week 4, and the incidence reached 100% at weeks 5 and 6. The number of skin nodules (multiplicity) in the 8-μg twice-weekly, 8-μg once-weekly, 4-μg twice-weekly, and 4-μg once-weekly groups was 62.4, 46.2, 62.6, and 36.9, respectively. The non-Tg mice also developed skin nodules, but the sensitivity to induction in the rasH2 Tg mice was higher. No nodules were observed in the acetone groups, but single nodules were apparent in the no-treatment rasH2 Tg and non-Tg groups. In conclusion, skin promotion effects could be detected within only 8 weeks in the rasH2 mice, and the concentration of 4 μg TPA once weekly was sufficient as a positive control. This short-term skin carcinogenesis bioassay using rasH2 mice could represent a useful tool for the assessment of drug and chemical safety with cutaneous treatment.

Behavioral genetics of the depression/cancer correlation: a look at the Ras oncogene family and the 'cerebral diabetes paradigm'

This study investigates the causes of the observed linkage between depression and later onset of cancer. The prevailing view is that cancer in depressed patients results from a weakened immune system. However, molecular biologists have recognized that dysregulation of the ras proto-oncogene results in impaired serotonin and dopamine synthesis manifesting as major depression. A qualitative review of the literature showed that (1) studies using the Minnesota Multiphasic Personality Inventory showed a greater correlation between depression and later cancer onset than those employing other measures and (2) the more related the cancer type was to the Ras oncogene family, the greater the correlation between depression and later cancer onset. These results support the hypothesis that the ras proto-oncogene plays a role in the etiology of depression and could be the common denominator in long-observed depression/cancer linkages. Previous depression/cancer linkage studies are confounded in that they failed to analyze cancer type and accurately diagnose depression.

Mouse skin models for carcinogenic hazard identification: utilities and challenges

This report addresses 1) the predictability of mouse skin models for carcinogenic hazard identification, 2) the association between early changes in the skin and later tumorigenic responses, and 3) the relative sensitivity of three mouse models of skin tumorigenesis; i.e. the genetically-initiated Tg.AC and RasH2 lines and the SENCAR mouse model. All three mouse models responded similarly, with mild inflammation and epidermal hyperplasia, to several weeks of treatment with a topical agent. Based on our previous research experience, we hypothesized that inflammation, irritation, proliferation, and/or hyperplasia in the skin would precede and predict the appearance of tumors in these sensitive mouse skin models. Consistent with our hypothesis, the test agent caused a low but significant tumorigenic response in Tg.AC mice. We propose that inflammation, irritation, and hyperplasia are sensitive predictors of a later tumorigenic response in Tg.AC mice. Further studies are needed, however, to better determine the relative sensitivity of these 3 models to a wider variety of agents.

Decreased c-kit function inhibits enhanced skin carcinogenesis in c-Ha-ras protooncogene transgenic mice

We previously showed that rasH2 transgenic mice carrying the human c-Ha-ras protooncogene are highly susceptible to chemical skin carcinogenesis. In the dermis of rasH2 mice, mast cells are recruited constitutively, and the number of mast cells increases more than in wild-type mice in response to treatment with 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. To determine whether enhanced skin tumor development in rasH2 mice is dependent on the recruitment of mast cells, we generated rasH2 KIT(W/Wv) mice by crossing rasH2 mice and W or W(v) KIT mutants, and examined the chemical skin carcinogenesis. In rasH2 KIT(W/Wv) mice, mast cells were not found in the dermis either before or after treatment with 7,12-dimethylbenz[a]anthracene and 12-O-tetradecanoylphorbol-13-acetate. Papilloma multiplicity was up to 4.6-fold higher in rasH2 KIT(+/+) mice compared with their rasH2 KIT(W/Wv) siblings. At 12 weeks after the experiment began, the volumes of tumors were significantly smaller in rasH2 KIT(W/Wv) relative to rasH2 KIT(+/+) mice (rasH2 KIT(W/Wv): 29.2 +/- 19.9 mm(3) versus rasH2 KIT(+/+): 179.6 +/- 726.6 mm(3); P = 0.0153). There was no difference in the latency or multiplicity of papillomas between mice without the rasH2 transgene, KIT(W/Wv) mice and their wild-type littermates. Western blot analysis showed that expression of H-RAS protein in the skin was equivalent in rasH2 KIT(W/Wv) and rasH2 KIT(+/+) mice. In conclusion, the inhibition of c-kit decreased H-ras-induced skin carcinogenesis. The suppression of c-kit may be a unique and effective target as a preclinical model of cancer treatment where the activation of H-ras has a significant role. Targeting mast cells could also be a potential strategy for treating malignancies.