Defective Jak-STAT signal transduction pathway in melanoma cells resistant to growth inhibition by interferon-alpha.

Advanced malignant melanoma is an aggressive malignancy with poor prognosis. Current therapeutic strategies have a modest success rate. The most promising treatment consists of a combination of chemotherapy with interferon-alpha, but complete response rates remain less than 15%. Interferon-alpha is also effective in adjuvant therapy for non-advanced melanoma treated surgically. The molecular mechanisms leading to loss of growth restraints and gain of growth-promoting functions during carcinogenesis of malignant melanoma are not understood in detail. Here, we studied 9 human melanoma cell lines with regard to growth inhibition by interferon-alpha and defects in intracellular signal transduction through the Jak-STAT pathway. In 3 cell lines, we found a complete loss of growth restraint by interferon-alpha. In all of them, different components of the Jak-STAT pathway were defective. Since signal transduction through the Jak-STAT pathway is necessary for antiviral and antiproliferative effects of interferons, we conclude that defects in this pathway may be one of the mechanisms that lead to cancer progression through loss of growth-restraining functions. Moreover, our results indicate that a subgroup of melanomas could be completely resistant to interferon-alpha and should therefore not be treated with this cytokine.

Identification of functional GRP-preferring bombesin receptors on human melanoma cells.

Bombesin was originally isolated from amphibian skin, whereas its mammalian counterpart, gastrin-releasing peptide (GRP), was first identified in the nervous system of the gastrointestinal tract. Whether GRP is present in the human skin is not known. Bombesin-like peptides are also known to modulate growth. We therefore investigated whether human melanoma cell lines express functional GRP-preferring bombesin receptors and whether they alter growth or other specific cellular functions of these tumour cells. GRP receptor mRNA was found in HBL, D-10, Me-28 and A375-6 cell lines, but only A375-6 cells express a large number of high-affinity binding sites for [125I]-[Tyr4] bombesin (K(d) 0.31 +/- 0.04 nmol L(-1), 3880 +/- 429 binding sites per cell). Bombesin dose-dependently increased cytosolic calcium, but did not alter interleukin (IL) 1beta-induced reduction of cell viability or IL-6 secretion, both A375-6-specific cell functions. Growth of A375-6 cells was not altered by bombesin or the specific GRP receptor antagonist BIM26226 as measured by [3H]-thymidine incorporation or methylene blue assay, whereas insulin alone or in combination with other potential growth factors dose-dependently stimulated growth of these cells. The newly characterized GRP-preferring bombesin receptors on highly malignant human melanoma cells could initiate studies of growth effects on solid tumours or in vivo scanning using radiolabelled tracers.