SummaryNeural cell adhesion molecule (NCAM) has recently been found on adult stem cells, but its biological significance remains largely unknown. In this study, we used bone-marrow-derived mesenchymal stem cells (MSCs) from wild-type and NCAM knockout mice to investigate the role of NCAM in adipocyte differentiation. It was demonstrated that NCAM isoforms 180 and 140 but not NCAM-120 are expressed on almost all wild-type MSCs. Upon adipogenic induction, Ncam -/-MSCs exhibited a marked decrease in adipocyte differentiation compared with wild-type cells. The role of NCAM in adipocyte differentiation was also confirmed in NCAM-silenced preadipocyte 3T3-L1 cells, which also had a phenotype with reduced adipogenic potential. In addition, we found that Ncam -/-MSCs appeared to be insulin resistant, as shown by their impaired insulin signaling cascade, such as the activation of the insulin-IGF-1 receptor, PI3K-Akt and CREB pathways. The PI3K-Akt inhibitor, LY294002, completely blocked adipocyte differentiation of MSCs, unveiling that the reduced adipogenic potential of Ncam -/-MSCs is due to insulin resistance as a result of loss of NCAM function. Furthermore, insulin resistance of Ncam -/-MSCs was shown to be associated with induction of tumor necrosis factor (TNF-), a key mediator of insulin resistance. Finally, we demonstrated that re-expression of NCAM-180, but not NCAM-140, inhibits induction of TNF- and thereby improves insulin resistance and adipogenic potential of Ncam -/-MSCs. Our results suggest a novel role of NCAM in promoting insulin signaling and adipocyte differentiation of adult stem cells. These findings raise the possibility of using NCAM intervention to improve insulin resistance.
The neural cell adhesion molecule (NCAM) was recently shown to be involved in the progression of various tumors with diverse effects. We previously demonstrated that NCAM potentiates the cellular invasion and metastasis of melanoma. Here we further report that the growth of melanoma is obviously retarded when the expression of NCAM is silenced. We found that the proliferation of murine B16F0 melanoma cells, their colony formation on soft agar, and growth of transplanted melanoma in vivo are clearly inhibited by the introduction of NCAM siRNA. Interestingly, change of NCAM expression level is shown to regulate the activity of Wnt signaling molecule, -catenin, markedly. This novel machinery requires the function of FGF receptor and glycogen synthase kinase-3 but is independent of the Wnt receptors, MAPK-Erk and PI3K/Akt pathways. In addition, NCAM is found to form a functional complex with -catenin, FGF receptor, and glycogen synthase kinase-3. Moreover, up-regulation of NCAM140 and NCAM180 appears more potent than NCAM120 in activation of -catenin, suggesting that the intracellular domain of NCAM is required for facilitating the -catenin signaling. Furthermore, the melanoma cells also exhibit distinct differentiation phenotypes with the NCAM silencing. Our findings reveal a novel regulatory role of NCAM in the progression of melanoma that might serve as a new therapeutic target for the treatment of melanoma.Melanoma arises from skin neural crest-derived pigmented melanocytes and accounts for around 80% of mortality of skin cancer (1) with less than 5% of a 5-year survival rate (2). The rapid growth of melanoma cells by overriding senescence and activation of pro-proliferating signal transduction were shown to play a key role in the development of melanoma into metastatic stage (3). Even though many cell growth promoting factors have been identified to be involved in the progression of melanoma and targeted for therapeutic intervention, the treatment efficacy of advanced melanoma with vertical growth and metastasis has not been significantly improved over the past few decades (1). Hence, further study to elucidate the molecular mechanisms underlying the proliferation of melanoma cells is required for the finding of novel potential intervention targets to improve the treatment of melanoma.It has been demonstrated that the adhesion molecules that mediate intercellular and cell-matrix interactions extensively participate in the progression of melanoma (4, 5) by altering the adhesion status and signal transduction of the cells. Neural cell adhesion molecule (NCAM), 2 a member of the immunoglobulin superfamily, has been well characterized in cell proliferation, differentiation, migration, neurite outgrowth, and synaptic plasticity in the nervous system (6 -9). However, recent studies have also revealed that the expression of NCAM drastically fluctuates in many tumors and affects tumor progression and prognosis (10). In small cell lung cancer (11) and the majority of multiple myelomas (12), the up-regulation of NC...
NG2-expressing neural progenitors can produce neurons in the central nervous system, providing a potential cell resource of therapy for neurological disorders. However, the mechanism underlying neuronal differentiation of NG2 cells remains largely unknown. In this report, we found that a thrombospondin (TSP) family member, TSP4, is involved in the neuronal differentiation of NG2 cells. When TSP4 was overexpressed, NG2 cells underwent spontaneous neuronal differentiation, as demonstrated by the induction of various neuronal differentiation markers such as NeuN, Tuj1, and NF200, at the messenger RNA and protein levels. In contrast, TSP4 silencing had an opposite effect on the expression of neuronal differentiation markers in NG2 cells. Next, the signaling pathway responsible for TSP4-mediated NG2 cell differentiation was investigated. We found that ERK but not p38 and AKT signaling was affected by TSP4 overexpression. Furthermore, when ERK signaling was blocked by the inhibitor U0126, the neuronal marker expression of NG2 cells was substantially increased. Together, these findings suggested that TSP4 promoted neuronal differentiation of NG2 cells by inhibiting ERK/MAPK signaling, revealing a novel role of TSP4 in cell fate specification of NG2 cells.
Oligodendrocytes (OLs) are derived oligodendrocyte progenitor cells (OPCs), and their differentiation is a tightly regulated process. It is known that cyclin-dependent kinases (CDKs) play an essential role as regulators of OPC differentiation. Here, we newly identified a CDK-like protein, PFTK1, to be involved in OPC differentiation. With serum-deprivation, OLN-93 undergoes OL differentiation, and PFTK1 expression is markedly decreased during differentiation. When PFTK1 is silenced, OL differentiation is potentiated, as suggested by the increase of various differentiation markers CNPase, MOG, CGT, and MBP, by qPCR and Western blotting analysis. Vice versa, PTTK1 overexpression has opposite effects on OL differentiation of OLN-93 in vitro. Next, the modulation mechanism underlying OL differentiation of OLN-93 was investigated. Significantly, PFTK1 silencing leads to the activation of PI3K/AKT pathway, but no activation of MAPK/ERK pathway. The inhibition of AKT by its specific inhibitor abrogates PFTK1 silencing-promoted OL differentiation, indicating that PFTK1 negatively regulates OL differentiation through PI3K/AKT pathway. Together, these findings indicate a novel role played by PFTK1 in OL development, thus presenting opportunities to establish therapeutic approaches in improving neurological recovery related to demyelinating disorders.
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