Downregulation of reversion-inducing cysteine-rich protein with Kazal motifs in malignant melanoma: Inverse correlation with membrane-type 1-matrix metalloproteinase and tissue inhibitor of metalloproteinase 2

Melanoma is the highly aggressive neoplasm that emerges from melanocytes, the melanin-producing cells present in skin and eyes. Melanocytes are confined to the epidermis, separated from the dermis by the basement membrane 1. Malignant transformants often gain the ability to invade this basement membrane and reach the blood vessels in the dermis, which is an important step toward the formation of metastases. This invasive process is frequently credited to increased activity of matrix metalloproteinases (MMPs) 2.

MMPs comprise a family of zinc-dependent endopeptidases involved in extracellular matrix (ECM) degradation that occurs in both physiological and pathological processes 3,4. MMPs may be soluble or membrane-bound, being produced by cells in an inactive form and activated in the extracellular environment by the proteolytic cleavage of an N-terminal propeptide 4. Cancer-related MMPs include MMP-2, MMP-9, and membrane-type (MT) 1-MMP 2,5. These metalloproteinases are widely associated with tumor aggressiveness, the tendency to undergo metastasis, and poor outcome of several types of malignancy 2, including melanoma 6.

MMP-mediated ECM degradation is regulated in a spatial-temporal manner, depending on the balance between MMPs and their inhibitor molecules, namely, tissue inhibitors of metalloproteinases (TIMPs) and reversion-inducing cysteine-rich protein with Kazal motifs (RECK).

TIMPs are soluble inhibitors of metalloproteinases. Four TIMPs have been described in mammals, each with its own tissue-specific expression and capacity to inhibit a given set of MMPs 3. TIMP-1, TIMP-2, and TIMP-3 are expressed in melanoma, but their role in tumors has been controversial. Expression of TIMPs has been shown to prevent tumors from metastasizing by inhibiting MMP activity 7. In contrast, other studies have shown that TIMPs have regulatory roles independent of their MMP-inhibitor activity, such as growth promoting and apoptosis inhibition 7,8.

Differently from TIMPs, RECK is a membrane-bound MMP-inhibitor 9,10. This glycosylphosphatidylinositol-anchored 971 aa has been shown to prevent ECM proteolysis by regulating key MMPs 11. Specifically, RECK inhibits MMP-9 transcription 12, secretion, and propeptide cleavage 9. RECK also inhibits the activation of pro-MMP-2, by interfering with the activation complex formed by MT1-MMP and TIMP-2 10.

MMP inhibition promoted by RECK affects cell behavior in a variety of contexts. Tumors expressing higher levels of RECK are less invasive and less prone to malignancy, reflecting a better prognosis 9,13–18. However, despite the fact that MMPs involvement in melanoma invasion and metastasis have been extensively described 6,19,20, RECK expression status in melanoma has not yet been clarified. Knowing that MMPs and TIMPs are involved in melanoma establishment and progression, the aim of this study is to verify how the expression of the novel MMP inhibitor RECK is modulated during melanoma progression, and whether the expression profile of this subset of genes (MMPs and their inhibitors) may be used as a diagnostic and prognostic tool.