NOV (nephroblastoma overexpressed) also known as CCN3 is a matricellular protein that in humans is encoded by the NOVgene.[5][6]
CCN family
NOV is a member of the CCN family of secreted, extracellular matrix (ECM)-associated signaling proteins (see also CCN intercellular signaling protein).[7][8] The CCN acronym is derived from the first three members of the family being identified, namely CYR61 (cysteine-rich angiogenic inducer 61, or CCN1), CTGF (connective tissue growth factor, or CCN2), and NOV. These proteins, together with WISP1 (CCN4), WISP2 (CCN5), and WISP3 (CCN6) comprise the six-member CCN family in vertebrates and have been renamed CCN1-6 in the order of their discovery by international consensus.[9]
Structure
The human NOV protein contains 357 amino acids with an N-terminal secretory signal peptide followed by four structurally distinct domains with homologies to insulin-like growth factor binding protein (IGFBP), von Willebrand type C repeats (vWC), thrombospondin type 1 repeat (TSR), and a cysteine knot motif within the C-terminal (CT) domain.[10][11]
NOV can bind BMP2 and inhibit its functions in promoting osteogenic differentiation,[19] and stimulate osteoclastogenesis through a process that may involve calcium flux.[20] Overexpression of Nov in transgenic mice in osteoblasts antagonizes both BMP and Wnt-signaling and result in osteopenia.[21]
In February 2017, it was reported that the NOV protein was involved in regulatory T cell-mediated oligodendrocytedifferentiation in the regeneration of myelin following damage to the myelin sheath. This finding revealed a new function for regulatory T cells that is distinct from their role in immunomodulation.[22] NOV (CCN3) has recently been implicated in mood disorders, notably in the postpartum period; these effects may be mediated by its effects on myelination [23]
Role in embryo development
In contrast to the lethality of Cyr61 (CCN1) and Ctgf (CCN2) genetic knockout in mice, Nov-null mice are viable and largely normal, exhibiting only modest and transient sexually dimorphic skeletal abnormalities.[24] However, Nov-null mice show enhanced blood vessel neointimal thickening when challenged with vascular injury, indicating that NOV inhibits neoinitimal hyperplasia.[25]
Role in cancer
Although NOV inhibits the proliferation of cancer cells,[26] it appears to promote metastasis.[27][28] Nov overexpression results in reduced tumor size in glioma cells xenografts,[29] but enhances metastatic potential in xenotransplanted melanoma cells.[30] NOV expression is associated with a higher risk of metastasis and worse prognosis in patients with cancers such as Ewing's sarcoma, melanoma, and breast cancer.[31] In chronic myeloid leukemia (CML), NOV is downregulated as a consequence of the kinase activity of BCR-ABL, a chimeric protein generated through the chromosomal translocation between chromosome 9 and 22.[32] Forced expression of NOV inhibits proliferation and restores growth control in CML cells, suggesting that NOV may be an alternate target for novel therapeutics against CML.[7][33]
^"Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^"Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
^Martinerie C, Viegas-Pequignot E, Guenard I, Dutrillaux B, Nguyen VC, Bernheim A, Perbal B (Dec 1992). "Physical mapping of human loci homologous to the chicken nov proto-oncogene". Oncogene. 7 (12): 2529–34. PMID1334251.
^Ellis PD, Metcalfe JC, Hyvönen M, Kemp PR (2003). "Adhesion of endothelial cells to NOV is mediated by the integrins alphavbeta3 and alpha5beta1". Journal of Vascular Research. 40 (3): 234–43. doi:10.1159/000071887. PMID12902636. S2CID84511515.
^Perbal B, Lazar N, Zambelli D, Lopez-Guerrero JA, Llombart-Bosch A, Scotlandi K, Picci P (Oct 2009). "Prognostic relevance of CCN3 in Ewing sarcoma". Human Pathology. 40 (10): 1479–86. doi:10.1016/j.humpath.2009.05.008. PMID19695675.