The apoptosis modulator and tumour suppressor protein RBM5 is a phosphoprotein.
RBM5/LUCA-15/H37 is a nuclear SR-related RNA binding protein with the ability to modulate both apoptosis and the cell cycle, and retard tumour formation. How RBM5 functions to carry out these, potentially interrelated, biological activities is unknown. Since reversible phosphorylation has been shown to play an important role in the regulation of SR protein function, apoptosis and cell cycle control, in an attempt to elucidate the underlying mechanisms regulating RBM5 function, the phosphorylation status of RBM5 was investigated. Whole cell lysate from growing cell cultures was treated with the broad phosphatase spectrum of CIP, resulting in a decrease in the molecular mass of RBM5. A similar decrease in molecular mass, of a subset of RBM5 proteins, was observed during growth factor deprivation, in a manner consistent with partial dephosphorylation of RBM5. Molecular mass increased upon growth factor addition, demonstrating that this apoptosis-associated alteration in molecular mass was a reversible process. Immunoprecipitation and mutagenesis experiments strongly suggested that phosphotyrosines are not present in RBM5 under normal growth conditions, and that serine 69 is phosphorylated, but not by Akt kinase. Taken together, these results suggest that reversible phosphorylation of RBM5 is a mechanism capable of regulating RBM5 participation in modulating apoptosis, and perhaps tumour suppression.
Shu
Yanjun
Y
Tumour Biology Group, Regional Cancer Program of the Hôpital régional de Sudbury Regional Hospital, Sudbury, Ontario, Canada.
Rintala-Maki
Nina D
ND
Wall
Vanessa E
VE
Wang
Ke
K
Goard
Carolyn A
CA
Langdon
Colleen E
CE
Sutherland
Leslie C
LC
D000595:Amino Acid Sequence; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D016147:Genes, Tumor Suppressor / Q000502:physiology*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins; D012694:Serine / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D010750:Phosphoproteins; C473448:RBM5 protein, human; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D012694:Serine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D017868:Cyclic AMP-Dependent Protein Kinases; D017869:Cyclic GMP-Dependent Protein Kinases; D011493:Protein Kinase C