Differential Expression of Vascular Endothelial Growth Factor–A Isoforms at Different Stages of Melanoma Progression

Abstract

Vascular endothelial growth factor-A (VEGF-A) is an important mediator of angiogenesis in normal and neoplastic tissues. Total VEGF-A levels have been associated with melanoma progression, but the relative contributions of each isoform is unknown. To determine whether differences in the production of any or all of the major VEGF-A isoforms are related to stage of progression, we compared message levels for the three major isoforms of VEGF in melanoma specimens from different stages of progression. Primary melanomas (N = 18), primary recurrences (N = 5), regional dermal metastases (N = 11), nodal metastases (N = 12), normal lymph nodes (N = 18), and distant metastases (N = 9) were prospectively collected. Samples from the horizontal and vertical growth phases of primary tumors were also collected from five additional patients. Message levels for the three major VEGF-A isoforms were measured using real-time quantitative reverse–transcriptase polymerase chain reaction and normalized to β-actin mRNA levels. There was a marked increase in the expression of all three VEGF-A isoforms from the vertical growth phase tissue as compared with the horizontal growth phase tissue. Primary tumors, local recurrences, regional dermal metastases, nodal metastases, and distant metastases all produced more VEGF₁₂₁ and VEGF₁₆₅ than negative nodes. Nodal metastases produced the highest level of these two isoforms, higher even than distant metastases. There was no significant difference in VEGF₁₈₉ message among the groups. Melanomas in the vertical growth phase produce more VEGF-A (all isoforms) than in the horizontal growth phase. Nodal metastases produce the highest levels of VEGF₁₂₁ and VEGF₁₆₅, but not VEGF₁₈₉ as compared with other stages of progression. These data suggest that the soluble forms of VEGF-A might be an important factor in melanoma metastasis to regional lymph nodes.