title: p85alpha regulates osteoblast differentiation by cross-talking with the MAPK pathway.
abstract: Class IA phosphoinositide 3-kinase (PI3K) is involved in regulating many cellular functions including cell growth, proliferation, cell survival, and differentiation. The p85 regulatory subunit is a critical component of the PI3K signaling pathway. Mesenchymal stem cells (MSC) are multipotent cells that can be differentiated into osteoblasts (OBs), adipocytes, and chondrocytes under defined culture conditions. To determine whether p85α subunit of PI3K affects biological functions of MSCs, bone marrow-derived wild type (WT) and p85α-deficient (p85α(-/-)) cells were employed in this study. Increased cell growth, higher proliferation rate and reduced number of senescent cells were observed in MSCs lacking p85α compare with WT MSCs as evaluated by CFU-F assay, thymidine incorporation assay, and β-galactosidase staining, respectively. These functional changes are associated with the increased cell cycle, increased expression of cyclin D, cyclin E, and reduced expression of p16 and p19 in p85α(-/-) MSCs. In addition, a time-dependent reduction in alkaline phosphatase (ALP) activity and osteocalcin mRNA expression was observed in p85α(-/-) MSCs compared with WT MSCs, suggesting impaired osteoblast differentiation due to p85α deficiency in MSCs. The impaired p85α(-/-) osteoblast differentiation was associated with increased activation of Akt and MAPK. Importantly, bone morphogenic protein 2 (BMP2) was able to intensify the differentiation of osteoblasts derived from WT MSCs, whereas this process was significantly impaired as a result of p85α deficiency. Addition of LY294002, a PI3K inhibitor, did not alter the differentiation of osteoblasts in either genotype. However, application of PD98059, a Mek/MAPK inhibitor, significantly enhanced osteoblast differentiation in WT and p85α(-/-) MSCs. These results suggest that p85α plays an essential role in osteoblast differentiation from MSCs by repressing the activation of MAPK pathway.
authors.affiliation: Department of Pediatrics, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Wu
authors.forename: Shi
authors.initials: S
authors.lastname: Chen
authors.forename: Selina A
authors.initials: SA
authors.lastname: Orlando
authors.forename: Jin
authors.initials: J
authors.lastname: Yuan
authors.forename: Edward T
authors.initials: ET
authors.lastname: Kim
authors.forename: Veerendra
authors.initials: V
authors.lastname: Munugalavadla
authors.forename: Raghuveer S
authors.initials: RS
authors.lastname: Mali
authors.forename: Reuben
authors.initials: R
authors.lastname: Kapur
authors.forename: Feng-Chun
authors.initials: FC
authors.lastname: Yang
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002867:Chromones / Q000494:pharmacology; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000235:genetics / Q000378:metabolism*; D056741:Cyclin D / Q000235:genetics / Q000378:metabolism; D019927:Cyclin E / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000201:enzymology*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D002867:Chromones; D056741:Cyclin D; D019927:Cyclin E; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D058543:Class Ia Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D020929:Mitogen-Activated Protein Kinase Kinases; D000469:Alkaline Phosphatase; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one