Anoxia-induced up-regulation of interleukin-8 in human malignant melanoma - A potential mechanism for high tumor aggressiveness

Besides its proinflammatory properties, interleukin-8 (IL-8) has been sugge sted as an important promoter for melanoma growth. To study the role of IL- 8 in melanoma biology, we determined the in vivo expression of IL-8 mRNA by in situ hybridization in primary melanoma lesions and metastases. High lev els of melanoma cell-associated IL-8-specific transcripts were exclusively detected in close vicinity of necrotic/hypoxic areas of melanoma metastases , whereas both in primary melanomas and in non-necrotic metastases IL-8 exp ression was low or absent. To analyze further the up-regulation of IL-8 mRN A expression in necrotic/hypoxic tumor areas, human melanoma cell lines of different aggressiveness exposed to severe hypoxic stress (anoxia) were use d as an in vitro model. Anoxia induced IL-8 mRNA and protein expression in the highly aggressive/metastatic cell lines MV3 and BLM but not in the low aggressive cell Lines IF6 and 530. As shown by IL-8 promoter-dependent repo rter gene analysis and mRNA stability assays, elevated mRNA levels in melan oma cells were due to both enhanced transcriptional activation and enhanced IL-8 mRNA stability. interestingly, transcriptional activation was abolish ed by mutations in the AP-1 and the NF-kappa B-like binding moths, indicati ng that both sites are critical for IL-8 induction. Concomitantly, anoxia i nduced an enhanced binding activity of AP-1 and NF-kappa B transcription fa ctors only in the highly aggressive cells. From our in vitro and in vile da ta we suggest that anoxia-induced regulation of IL-8 might be a characteris tic feature of aggressive tumor cells, thus indicating that IL-8 might play a critical role for tumor progression in human malignant melanoma.