Expression of NGF/proNGF and Their Receptors TrkA, p75NTR and Sortilin in Melanoma

Abstract

There is increasing evidence that nerve growth factor (NGF) and its receptors, the neurotrophic receptor tyrosine kinase 1 (NTRK1/TrkA), the common neurotrophin receptor (NGFR/p75NTR) and the membrane receptor sortilin, participate in cancer growth. In melanoma, there have been some reports suggesting that NGF, TrkA and p75NTR are dysregulated, but the expression of the NGF precursor (proNGF) and its membrane receptor sortilin is unknown. In this study, we investigated the expression of NGF, proNGF, TrkA, p75NTR and sortilin by immunohistochemistry in a series of human tissue samples (n = 100), including non-cancerous nevi (n = 20), primary melanomas (n = 40), lymph node metastases (n = 20) and distant metastases (n = 20). Immunostaining was digitally quantified and revealed NGF and proNGF were expressed in all nevi and primary melanomas, and that the level of expression decreased from primary tumors to melanoma metastases (p = 0.0179 and p < 0.0001, respectively). Interestingly, TrkA protein expression was high in nevi and thin primary tumors but was strongly downregulated in thick primary tumors (p < 0.0001) and metastases (p < 0.0001). While p75NTR and sortilin were both expressed in most nevi and melanomas, there was no significant difference in expression between them. Together, these results pointed to a downregulation of NGF/ProNGF and TrkA in melanoma, and thus did not provide evidence to support the use of anti-proNGF/NGF or anti-TrkA therapies in advanced and metastatic forms of melanoma.

The Alternative TrkAIII Splice Variant, a Targetable Oncogenic Participant in Human Cutaneous Malignant Melanoma

“…The detection of intracellular TrkA and phosphorylated TrkA isoform immunoreactivity in CMMs in the present study extends previous reports that enhanced TrkA expression and intracellular phosphorylated TrkA immunoreactivity are associated with poor prognosis in CMM [9,10], but contrasts with a recent report that TrkA immunoreactivity is not associated with CMM progression [13]. This contradiction can be explained by the rabbit anti-human TrkA monoclonal anti-TrkA antibody (14G6, CS-2508, Cell Signaling) used in the latter study [13], raised against a synthetic peptide surrounding TrkA arginine 220 within the D4 domain, which would detect fully spliced TrkA but not TrkAIII [14].…”

“…The detection of intracellular TrkA and phosphorylated TrkA isoform immunoreactivity in CMMs in the present study extends previous reports that enhanced TrkA expression and intracellular phosphorylated TrkA immunoreactivity are associated with poor prognosis in CMM [9,10], but contrasts with a recent report that TrkA immunoreactivity is not associated with CMM progression [13]. This contradiction can be explained by the rabbit anti-human TrkA monoclonal anti-TrkA antibody (14G6, CS-2508, Cell Signaling) used in the latter study [13], raised against a synthetic peptide surrounding TrkA arginine 220 within the D4 domain, which would detect fully spliced TrkA but not TrkAIII [14]. The lack of immunoreactivity in metastatic CMMs reported using this antibody [13] suggests that the immunoreactivity detected in metastatic CMMs using antibodies that recognise non-phosphorylated and phosphorylated forms of both fully spliced TrkA and TrkAIII (this study and [9,10]) was in fact due to TrkAIII, which is supported by the detection of ≈100 kDa phosphorylated TrkAIII-like species in TrkAIII mRNA-expressing metastatic CMMs.…”

“…This contradiction can be explained by the rabbit anti-human TrkA monoclonal anti-TrkA antibody (14G6, CS-2508, Cell Signaling) used in the latter study [13], raised against a synthetic peptide surrounding TrkA arginine 220 within the D4 domain, which would detect fully spliced TrkA but not TrkAIII [14]. The lack of immunoreactivity in metastatic CMMs reported using this antibody [13] suggests that the immunoreactivity detected in metastatic CMMs using antibodies that recognise non-phosphorylated and phosphorylated forms of both fully spliced TrkA and TrkAIII (this study and [9,10]) was in fact due to TrkAIII, which is supported by the detection of ≈100 kDa phosphorylated TrkAIII-like species in TrkAIII mRNA-expressing metastatic CMMs.…”

“…TrkA mediates melanocyte and melanoma cell responses to neurotrophic factors [5,6], the gene that encodes TrkA, NTRK1, is frequently amplified in CMMs, increased TrkA expression and intracellular activation have been positively correlated with CMM progression and poor outcome [7][8][9][10] and TrkA fusion oncogenes have been detected in CMMs and spitzoid melanomas [11,12]. However, this possibility is contradicted by reports that TrkA inhibits melanoma cell proliferation and promotes differentiation, and it has been recently reported not to be associated with CMM metastatic progression, consistent with melanoma-suppressing potential [7,13]. This controversy is reminiscent of similar reports of TrkA's tumour-suppressing and oncogenic roles in neuroblastoma (NB) and NB cell lines [14][15][16][17].…”

Identification of upstream immunoregulators that target protein co-expression networks significantly associated with early-stage micropapillary/solid predominant lung adenocarcinomas

“…NGF and its receptors, such as the neurotrophic receptor tyrosine kinase 1 (NTRK1/TrkA), NGFR, and SORT1, participate in cancer growth. Expression of NGFR and SORT1 were upregulated in primary melanoma [21] and similar expression pro les of sortilin were reported in other cancers, including breast cancer, thyroid, and pancreatic cancer [21].…”