The significance of melanotropic hormones as physiologic regulators of cutaneous pigmentation in humans is still controversial. Until recently, no direct effect for melanotropins could be demonstrated on human melanocytes.Here we present conclusive evidence that a!-melanotropin (a-melanocyte-stimulating hormone, ai-MSH) and the related hormone corticotropin (adrenocorticotropic hormone, ACTH) stimulate the proliferation and melanogenesis of human melanocytes maintained in culture in a growth medium lacking any AMP inducer. The minimal effective dose of either hormone is 0.1 nM. In time-course experiments, the increase in cell number and tyrosinase activity became evident after one treatment of the melanocytes with 100 nM a-MSH for 48 hr. The mitogenic effect gradually increased to 50-270S% above control, depending on the individual melanocyte strain, with continuous treatment with 100 nM a-MSH for 8 days, whereas the melanogenic effect became maximal (70-450% increase above control) after 4 days oftreatment. Western blot analysis of tyrosinase and the tyrosinase-related proteins TRP-1 and TRP-2 revealed that a-MSH increased the expression of those three melanogenic proteins. This was not accompanied by any change in their mRNA levels after brief (1.5-24 hr) or prolonged (6 days) treatment with 100 nM a-MSH, suggesting that the increased expression of these melanogenic proteins was due to posttranscriptional events. These results demonstrate both mitogenic and melanogenic effects of a-MSH and ACTH on human melanocytes. That both hormones are effective at subnanomolar concentrations, combined with the presence of melanotropin receptors on human melanocytes, strongly suggests that these melanotropins play a physiologic role in regulating human cutaneous pigmentation.a-Melanotropin (a melanocyte-stimulating hormone, a-MSH) is the physiologic hormone that regulates integumental pigmentation of many vertebrate species. For example, a-MSH induces rapid skin darkening in amphibians and reptiles and stimulates follicular eumelanogenesis in the mouse (1,2). In addition to the pigmentary effects, other functions for a-MSH and related melanotropins have been described, such as the antagonistic interaction with interleukin 1 (3, 4) and trophic effects on neurons (5, 6

Senescence induction could be used as an effective treatment for hepatocellular carcinoma (HCC). However, major senescence inducers (p53 and p16 Ink4a) are frequently inactivated in these cancers. We tested whether transforming growth factor-b (TGF-b) could serve as a potential senescence inducer in HCC. First, we screened for HCC cell lines with intact TGF-b signaling that leads to small mothers against decapentaplegic (Smad)-targeted gene activation. Five cell lines met this condition, and all of them displayed a strong senescence response to TGF-b1 (1-5 ng/mL) treatment. Upon treatment, c-myc was down-regulated, p21Cip1 and p15 Ink4bwere up-regulated, and cells were arrested at G 1 . The expression of p16 Ink4a was not induced, and the senescence response was independent of p53 status. A short exposure of less than 1 minute was sufficient for a robust senescence response. Forced expression of p21Cip1 and p15Ink4b recapitulated TGF-b1 effects. Senescence response was associated with reduced nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) induction and intracellular reactive oxygen species (ROS) accumulation. The treatment of cells with the ROS scavenger N-acetyl-L-cysteine, or silencing of the NOX4 gene, rescued p21 Cip1 and p15 Ink4b accumulation as well as the growth arrest in response to TGF-b. Human HCC tumors raised in immunodeficient mice also displayed TGF-b1-induced senescence. More importantly, peritumoral injection of TGFb1 (2 ng) at 4-day intervals reduced tumor growth by more than 75%. In contrast, the deletion of TGF-b receptor 2 abolished in vitro senescence response and greatly accelerated in vivo tumor growth. Conclusion: TGF-b induces p53-independent and p16 Ink4a -independent, but Nox4-dependent, p21 Cip1-dependent, p15 Ink4b-dependent, and ROS-dependent senescence arrest in well-differentiated HCC cells. Moreover, TGF-b-induced senescence in vivo is associated with a strong antitumor response against HCC. (HEPATOLOGY 2010;52:966-974)

Background: -catenin mutations that constitutively activate the canonical Wnt signaling have been observed in a subset of hepatocellular carcinomas (HCCs). These mutations are associated with chromosomal stability, low histological grade, low tumor invasion and better patient survival. We hypothesized that canonical Wnt signaling is selectively activated in well-differentiated, but repressed in poorly differentiated HCCs. To this aim, we characterized differentiation status of HCC cell lines and compared their expression status of Wnt pathway genes, and explored their activity of canonical Wnt signaling.

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Abstract. Human breast cancer displays nuclear accumulation of ß-catenin and induction of cyclin D1 expression, which suggests that canonical Wnt/ß-catenin signaling is activated. In other cancers, the activation of canonical wnt/ß-catenin signaling is associated with APC, CTNNB1 or AXIN1 mutations. However, these mutations are rare or absent in breast cancer. WNT4, WNT6, WNT8B, WNT9A and WNT10B. In contrast, the expression of WNT5A, WNT5B and WNT16 was usually down-regulated. It is noteworthy that all six Wnt ligands that are overexpressed in malignant cell lines are known to signal through the canonical Wnt/ß-catenin signaling pathway, whereas down-regulated WNT5A and WNT5B ligands signal via the non-canonical pathway. The expression of both canonical Wnt ligands and most Frizzled receptors in breast cancer cell lines suggests that canonical Wnt/ß-catenin signaling is activated in these cell lines by an autocrine/ paracrine mechanism. In support of this prediction, we observed nuclear ß-catenin accumulation and cyclin D1 induction in breast cancer cell lines, but not in HMEC. These results imply that ligand-dependent canonical Wnt/ß-catenin signaling is active in human breast cancer.