ECTOPIC G-CSF EXPRESSION IN HUMAN-MELANOMA LINES MARKS A TRANSDOMINANT PATHWAY OF TUMOR PROGRESSION

Using a human melanoma/Scid xenograft model with the C8161, M24-met, L D-1 and other human melanoma lines to investigate spontaneous metastas is, we made the observation of marked splenomegaly (up to five times n ormal weight and size) in only those xenografts exhibiting high degree s of spontaneous metastasis, Evaluation of this revealed the cause to be massive myelopoiesis due to ectopic granulocyte/colony-stimulating factor (G-CSF) production by the melanoma cells, Because of these obse rvations linking G-CSF expression with metastasis of human melanoma, w e decided to investigate the mechanism of this ectopic production. No gross amplification or rearrangement of the G-CSF gene could be detect ed as the basis for the increased transcriptional activity in any of t hese lines. Human-human somatic cell hybridization studies carried out between the metastatic C8161 and several different nonmetastatic non- G-CSF-expressing lines revealed, in addition to metastatic dominance, 3- to 10-fold enhancement of G-CSF transcription and expression in the fusions compared with C8161 itself. The suggestion of a trans-dominan t mechanism was further supported by transfection studies with a human G-CSF promoter-CAT-reporter construct, which revealed 3- to 5-fold in creased reporter activity in only those melanoma lines and hybrids exp ressing G-CSF, Furthermore, no obvious autocrine or paracrine effects of this ectopic G-CSF expression on the melanoma lines' growth or meta stasis were apparent, as all of the G-CSF-expressing lines lacked the G-CSF receptor and injections of purified recombinant G-CSF exerted no stimulatory effects on their tumorigenicity, latency, growth, or meta stasis in Scid mice. Thus, we advance the hypothesis that G-CST expres sion is serving as a marker of a more generalized trans-dominant pathw ay linked to tumor progression and metastasis. This hypothesis has dir ect relevance to many human cancers where ectopic hormone or growth fa ctor production occurs with no obvious autocrine or paracrine benefit to the tumor.