Tumor progression of skin carcinoma cells in vivo promoted by clonal selection, mutagenesis, and autocrine growth regulation by granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor

Tumor microenvironment is crucial for cancer growth and progression as evid enced by reports on the significance of tumor angiogenesis and stromal cell s. Using the HaCaT/HaCaT-ras human skin carcinogenesis model, we studied tu mor progression from benign tumors to highly malignant squamous cell carcin omas. Progression of tumorigenic HaCaT-ras clones to more aggressive and ev entually metastatic phenotypes was reproducibly achieved by their in vivo g rowth as subcutaneous tumors in nude mice. Their enhanced malignant phenoty pe was stably maintained in recultured tumor cells that represented, identi fied by chromosomal analysis, a distinct subpopulation of the parental line . Additional mutagenic effects were apparent in genetic alterations involvi ng chromosomes 11 and 2, and in amplification and overexpression of the H-r as oncogene. Importantly, in vitro clonal. selection of benign and malignan t cell lines never resulted in late-stage malignant clones, indicating the importance of the in vivo environment in promoting an enhanced malignant ph enotype. Independently of their H-ras status, all in vivo-progressed tumor cell lines (five of five) exhibited a constitutive and stable expression of the hematopoietic growth factors granulocyte colony-stimulating factor and granulocyte-macrophage colony-stimulating factor, which may function as au tocrine/paracrine mediators of tumor progression in vivo. Thus, malignant p rogression favored by the in vivo microenvironment requires both clonal sel ection of subpopulations. adapted to in vivo growth and mutational events l eading to stable functional alterations.