The chemokine receptor 4 (CXCR4) in primary cutaneous melanoma--correlation with established histopathologic prognosticators, BRAF status and expression of its ligand CXCL12
Mitchell, Brendon C.
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Dysregulation of the chemokine receptor 4 (CXCR4) and its primary ligand CXCL12 (SDF-1, stromal cell-derived factor-1), has been implicated in the progression of melanoma and the mechanisms by which the CXCR4/CXCL12 axis has been shown to activate cell cycle progression is via stimulation of the mitogen-activated protein kinase (MAPK) pathway. Given this, we sought to ascertain the potential cooperativity of CXCR4 with established histopathologic prognosticators including the BRAF status in primary cutaneous melanoma. In this IRB approved study, archived tissue samples with diagnosis of primary cutaneous melanoma were retrieved from the Skin Pathology Laboratory at BUSM, Boston, MA and a total of 107 cases identified as meeting criteria for inclusion. Protein expression of CXCR4 and CXCL12 were assessed using commercially available rabbit polyclonal antibodies (Ab2074 and, ab9797 respectively, Abcam, Cambridge, MA, USA). CXCR4 gene expression (mRNA) was measured by semiquantitative RT-PCR with appropriate controls. For IHC, a semi-quantitative scoring (ranging from 0-3) was used and cases with a score of ≥2 (>10%) were considered positive. Molecular analysis for CXCR4 gene expression and BRAF exon 15 mutation status was performed using mRNA semi-quantitative RT-PCR and DNA Sanger sequencing respectively. Univariate analyses of CXCR4 mRNA expression revealed a statistically significant correlation between elevated CXCR4 expression (low ΔCt value) and presence of the BRAF mutation and absence of a host response (p=0.03 and p=0.0003 respectively). Univariate analyses revealed a significant correlation between elevated CXCR4 mRNA (low ΔCt value) and the following: presence of BRAF mutation and absence of a host response (p=0.03 and 0.0003 respectively). CXCR4 mRNA was significantly higher among both AJCC stage 1 and stage 3 compared to stage 2 (p=0.01). Compared with CXCR4 negative samples, univariate analyses of CXCR4 protein showed that the proportion of CXCR4 positives was significantly greater in melanomas with absence of mitoses (p<0.0001), ulceration (p=0.0008) and regression (p=0.02). Patients presenting at shallower stages (AJCC 1-2) exhibited a larger proportion of CXCR4 positives (76.9%, p<0.0001 and 69.0%, p=0.004), while those at deeper stages (AJCC 3-4) exhibited a larger proportion of negatives (75.0%, p=0.002 and 66.7%, p=0.10). In a multivariable analysis, lower odds of CXCR4 protein expression were associated with AJCC stage-3 (OR=0.16, p=0.01), stage-4 (OR=0.17, p=0.04), and mitoses (OR=0.21, p=0.01). Lack of correlation between CXCR4 mRNA and protein expression suggests that further study is required for a more precise understanding of mRNA-protein interaction for CXCR4 in order to identify factors contributing to the lack of concordance. CXCR4 protein appears to be associated with established prognosticators of good clinical outcome as its expression is less frequently observed in melanomas with mitoses, ulceration and depth >2 mm. The association between CXCR4 mRNA and a brisk host response suggests that it may serve as a biomarker for recruiting melanoma patients for immunotherapy. Higher CXCR4 mRNA in patients with a BRAF mutation suggests its utility as a putative therapeutic target.