AMP-activated protein kinase (AMPK) is an energy-sensing kinase that has recently been shown to regulate the differentiation of preadipocytes and osteoblasts. However, the role of AMPK in stem cell differentiation is largely unknown. Using in vitro culture models, the present study demonstrates that AMPK is a critical regulatory factor for osteogenic differentiation. We observed that expression and phosphorylation of AMPK were increased during osteogenesis in human adipose tissue-derived mesenchymal stem cells (hAMSC). To elucidate the role of AMPK in osteogenic differentiation, we investigated the effect of AMPK inhibition or knockdown on mineralization of hAMSC. Compound C, an AMPK inhibitor, reduced mineralized matrix deposition and suppressed the expression of osteoblast-specific genes, including alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), and osteocalcin (OCN). Knockdown of AMPK by shRNA-lentivirus infection also reduced osteogenesis. In addition, inhibition or knockdown of AMPK during osteogenesis inhibited ERK phosphorylation, which is required for osteogenesis. Interestingly, inhibition of AMPK induced adipogenic differentiation of hAMSC, even in osteogenic induction medium (OIM). These results provide a potential mechanism involving AMPK activation in osteogenic differentiation of hAMSC and suggest that commitment of hAMSC to osteogenic or adipogenic lineage is governed by activation or inhibition of AMPK, respectively.

Retinoic acid (RA) is one of the major components of vitamin A.In the present study, we found that retinoic acid activated AMPactivated protein kinase (AMPK). RA induced Rac1-GTP formation and phosphorylation of its downstream target, p21-activated kinase (PAK), whereas the inhibition of AMPK blocked RA-induced Rac1 activation. Moreover, cofilin, an actin polymerization regulator, was activated when incubated with RA. We then showed that inhibition of AMPK by compound C, a selective inhibitor of AMPK, or small interfering RNA of AMPK ␣1 blocked RA-induced cofilin phosphorylation. Additionally, we found that retinoic acid-stimulated glucose uptake in differentiated C2C12 myoblast cells and activated p38 mitogen-activated protein kinase (MAPK). Finally, the inhibition of AMPK and p38 MAPK blocked retinoic acid-induced glucose uptake. In summary, our results suggest that retinoic acid may have cytoskeletal roles in skeletal muscle cells via stimulation of the AMPK-Rac1-PAK-cofillin pathway and may also have beneficial roles in glucose metabolism via stimulation of the AMPK-p38 MAPK pathway.Retinoids are important regulators of differentiation and cell proliferation. Induction of differentiation by retinoic acid has been observed in various cell systems, such as endothelial, neuronal, and lung cancers (1). Retinoic acid has been shown to inhibit the growth of breast cancer cells and to reduce the number of tumors in animal models (2, 3). The anti-tumor potential of retinoids has been demonstrated by their ability to inhibit the growth of several human cancers, including colon cancer, prostate cancer, and melanoma (4, 5). Retinoic acid mediates its effects by binding to its receptors, retinoid acid receptor, or retinoid X receptor, followed by heterodimerization of the receptors and their recognition of binding to retinoid acid receptor element-containing promoters.AMP-activated protein kinase (AMPK) 2 is a phylogenetically conserved intracellular energy sensor that plays a central role in the regulation of glucose and lipid metabolism. AMPK, a heterotrimeric complex comprised of a catalytic subunit and two regulatory subunits, is activated when cellular energy is depleted (6). Upon activation by allosteric binding of AMP or phosphorylation at Thr 172 of the catalytic subunit by AMPK kinase, AMPK accelerates ATP-generating catabolic pathways, including glucose and fatty acid oxidation (7-9) while simultaneously reducing ATP-consuming anabolic pathways including cholesterol, fatty acid, and triacylglycerol synthesis (10). In addition to its roles in energy homeostasis, AMPK also has been shown to regulate the endothelial nitric-oxide synthase pathway through Rac1 (11). The involvement of interaction of Rac1 with AMPK has been implicated in many of the biological effects of AMPK in cytoskeletal remodeling.Small GTPases of the Rho family have diverse effects on cellular structure and function. Depending on the cell type, specific Rho GTPases induce particular surface protrusions generated by actin-remodeling reactions t...

Lysophosphatidic acid (LPA) is a bioactive phospholipid that affects various biological functions, such as cell proliferation, migration, and survival, through LPA receptors. Among them, the motility of cancer cells is an especially important activity for invasion and metastasis. Recently, AMP-activated protein kinase (AMPK), an energy-sensing kinase, was shown to regulate cell migration. However, the specific role of AMPK in cancer cell migration is unknown. The present study investigated whether LPA could induce AMPK activation and whether this process was associated with cell migration in ovarian cancer cells. We found that LPA led to a striking increase in AMPK phosphorylation in pathways involving the phospholipase C-␤3 (PLC-␤3) and calcium/calmodulin-dependent protein kinase kinase ␤ (CaMKK␤) in SKOV3 ovarian cancer cells. siRNA-mediated knockdown of AMPK␣1, PLC-␤3, or (CaMKK␤) impaired the stimulatory effects of LPA on cell migration. Furthermore, we found that knockdown of AMPK␣1 abrogated LPA-induced activation of the small GTPase RhoA and ezrin/radixin/moesin proteins regulating membrane dynamics as membrane-cytoskeleton linkers. In ovarian cancer xenograft models, knockdown of AMPK significantly decreased peritoneal dissemination and lung metastasis. Taken together, our results suggest that activation of AMPK by LPA induces cell migration through the signaling pathway to cytoskeletal dynamics and increases tumor metastasis in ovarian cancer. Lysophosphatidic acid (LPA)2 has been shown to participate in diverse biological actions, including changes in cell shape, motility, and proliferation, in a variety of cell types (1). Previous studies have shown that LPA has a role in early signaling events, such as Ca 2ϩ mobilization, changes in cAMP accumulation, and the activation of several protein kinases (1-4). Among these pathological processes, the role of LPA in ovarian cancer has been most extensively studied. LPA contributes to the development, progression, and metastasis of ovarian cancer, and its concentration is increased up to 80 M (in comparison to the basal 1-5 M concentration) in both plasma and ascites of ovarian cancer patients (5). In vitro studies have shown that production of LPA levels was constitutively increased in ovarian cancer cells but not in normal ovarian epithelial cells (6, 7). Moreover, in a study of the expression of LPA receptor mRNA and protein levels in ovarian cancer tissues, LPA 2 and LPA 3 were aberrantly up-regulated, but LPA 1 was not changed (8, 9). Overexpression of LPA 2 and LPA 3 are closely associated with tumor progression in ovarian cancer cells (10 -13). As evidence of intracellular signaling in cancer cell migration, LPA induces activation of Ras-MEKK1 (14), Rac1 (15), Ca 2ϩ -dependent Pyk2 (16), and the Rho/ROCK pathway (17), which indicates that dynamic cytoskeletal rearrangement in LPA-mediated cell migration is regulated through the coordination of complex contexts (such as small GTPases, focal adhesion, and Ca 2ϩ -dependent signaling). However, the exact re...