Immunohistochemical analysis of T-type calcium channels in acquired melanocytic naevi and melanoma

BACKGROUND

Cutaneous malignant melanoma arises from transformed melanocytes de novo or from congenital or acquired melanocytic naevi. We have recently reported that T-type Ca²⁺ channels (TT-Cs) are upregulated in human melanoma and play an important role in cell proliferation.

OBJECTIVES

To describe for the first time in formalin-fixed paraffin-embedded tissue the immunoexpression of TT-Cs in biopsies of normal skin, acquired melanocytic naevi and melanoma, in order to evaluate their role in melanomagenesis and/or tumour progression, their utility as prognostic markers and their possible use in targeted therapies.

METHODS

Tissue samples from normal skin, melanocytic naevi and melanoma were subjected to immunohistochemistry for two TT-Cs (Cav3.1, Cav3.2); markers of proliferation (Ki67), the cell cycle (cyclin D1), hypoxia (Glut1), vascularization (CD31) and autophagy (LC3); BRAF V600E mutation (VE1) and phosphatase and tensin homologue (PTEN). Immunostaining was evaluated by histoscore. In silico analysis was used to assess the prognostic value of TT-C overexpression.

RESULTS

TT-C immunoexpression increased gradually from normal skin to common naevi, dysplastic naevi and melanoma samples, but with differences in the distribution of both isoforms. Particularly, Cav3.2 expression was significantly higher in metastatic melanoma than in primary melanoma. Statistical correlation showed a linear interaction between PTEN loss/BRAF V600E/Cav3.1/LC3/ Ki67/cyclin D1/Cav3.2/Glut1. Disease-free survival (DFS) and overall survival correlated inversely with overexpression of Cav3.2. DFS also correlated inversely with overexpression of Cav3.1.

CONCLUSIONS

TT-C immunoexpression on melanocytic neoplasms is consistent with our previous in vitro studies and appears to be related to tumour progression. TT-C upregulation can be considered as a prognostic marker using The Cancer Genome Atlas database. The high expression of Cav3.2 in metastatic melanoma encourages the investigation of the use of TT-C blockers in targeted therapies.

Abstract S1-06: The miR-424/503 cluster is a breast cancer tumor suppressor with a role in chemoresistance

Recently, we have identified the miR-424(322)/503 cluster as an important regulator of mammary epithelial homeostasis. The miR-424(322)/503 cluster was identified as one of the few miRNAs significantly upregulated during involution after pregnancy. By generating a knock-out mouse model, we found that regression of the mammary epithelium after pregnancy was compromised in the absence of miR-424(322)/503. Mechanistically, our studies unveiled that miR-424(322)/503 is induced by the canonical TGF-β-SMAD pathway, and that it orchestrates changes in the mammary epithelium by downregulating the expression of key components of signal transduction (IGF1R) and apoptosis (BCL2) Llobet et al. Genes&Development 2014).

Remarkably, our new studies have revealed that miR-424(322)/503-/- female mice develop hyperplasia and mammary tumors that are promoted by pregnancy. Thus, we investigated the status of this cluster in human breast cancers. For this we analyzed the METABRIC dataset. These studies revealed that the miR-424(322)503 cluster was heterozygously deleted in ∼16% of breast cancers and that its deletion correlates with lower expression levels of the mature miRNA forms. Importantly, miR-424(322)/503 is located on the X-chromosome and we have confirmed that is monoallelically expressed due to X-chromosome inactivation. Thus, the mutation of the active allele strongly impacts the expression of the miR-cluster. Deletions of the miR-424(322)/503 locus were more frequent in molecular subtypes with aggressive behavior (Luminal B, HER2+ and Basal) and both deletions and low expression of the cluster were associated with poor prognosis and reduced survival.

Some of the miR-424(322)/503 targets that we have previously validated (BCL2 and IGF1R) are involved in resistance to chemotherapy. Thus, we investigated in vivo, utilizing our knock-out mouse model, if loss of miR-424(322)/503 induces resistance to chemotherapeutic drugs. For this we crossed our miR-424(322)/503-/- animals with the HER2+ model FVB/N-Tg(MMTVneu)202Mul/J. Tumors emerging in HER2+/miR-424(322)/503-/- animals presented higher levels of BCL2 and hyperactivation of the IGF1R-AKT signaling compared to HER2+/miR-424(322)/503+/+ counterparts. Furthermore, these tumors were resistant to standard chemotherapy. Importantly, inhibition of BCL2 with ABT-199 and IGF1R with BMS-754807, two compounds currently in clinical trial, completely reverted chemotherapy resistance.

Overall, our data present evidence supporting a tumor suppressor role for miR-424(322)/503 cluster and its implication in resistance to chemotherapy.

Citation Format: Silva J, Llobet-Navas D, Rodriguez-Barrueco R, Sanchez-Garcia F, Pe'er D. The miR-424/503 cluster is a breast cancer tumor suppressor with a role in chemoresistance. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr S1-06.