Expression of G1 phase regulators in MG-63 osteosarcoma cell line.
Cyclins and cyclin-dependent kinases (cdks) form complexes that govern transitions during cell cycle phases. In this study we characterized a human osteosarcoma cell line, MG-63, for the expression level of cyclin D1, cyclin E, cdk4, cdk2, and cell cycle inhibitors pRb and p21. To investigate the role of these proteins we treated MG-63 cells with tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). Cell proliferation analysis demonstrated an increased proliferation of MG-63 cells with IL-6, while TNF-alpha acted as an anti-proliferative agent. Immunoblotting revealed an increased expression of p21 with TNF-alpha and its complex with cdk2. TNF-alpha reduced the expression of the cyclin E-cdk2 complex. TNF-alpha did not affect the amount of cyclin D1, cyclin E, cdk4, cdk2, and of cyclin D1-cdk4 complex. IL-6 decreased p21 expression and its complex with cdk2, while it increased the cyclin E-cdk2 complex. Cyclin D1 and cdk4 expression and their complex did not change after IL-6 treatment, nor did cyclin E and cdk2 protein expression. Hyperphosphorylated/dephosphorylated Rb protein ratio was reduced with TNF-alpha whereas it increased with IL-6. These results may suggest an important role of p21 and of cyclin E-cdk2 complex in the G1 phase regulation through pRb phosphorylation in MG-63 cells.
Merli
M
M
Laboratory of Oncologic Research, Rizzoli Orthopaedic Institute, 40136 Bologna, Italy.
Benassi
M S
MS
Gamberi
G
G
Ragazzini
P
P
Sollazzo
M R
MR
Molendini
L
L
Magagnoli
G
G
Ferrari
C
C
Maltarello
M C
MC
Picci
P
P
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001859:Bone Neoplasms / Q000378:metabolism* / Q000473:pathology*; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins / Q000096:biosynthesis* / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D019938:Cyclin D1 / Q000096:biosynthesis / Q000502:physiology; D019927:Cyclin E / Q000096:biosynthesis / Q000502:physiology; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis / Q000502:physiology; D016213:Cyclins / Q000096:biosynthesis; D016193:G1 Phase / Q000502:physiology*; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology; D012516:Osteosarcoma / Q000378:metabolism* / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000502:physiology; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein / Q000096:biosynthesis; D013778:Tetrazolium Salts; D013844:Thiazoles; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D015850:Interleukin-6; D011518:Proto-Oncogene Proteins; D016160:Retinoblastoma Protein; D013778:Tetrazolium Salts; D013844:Thiazoles; D014409:Tumor Necrosis Factor-alpha; D019938:Cyclin D1; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; C022616:thiazolyl blue