Purification and identification of the STAT5 protease in myeloid cells

TY - JOUR

T1 - Purification and identification of the STAT5 protease in myeloid cells

AU - Schuster, B

AU - Hendry, L

AU - Byers, H

AU - Lynham, S F

AU - Ward, M A

AU - John, S

PY - 2007/5/15

Y1 - 2007/5/15

N2 - STAT (signal transducer and activator of transcription) proteins are critical regulators of cytokine-induced cell proliferation, differentiation and survival. STAT functional activity can be variably regulated by post-translational modifications, including phosphorylation, acetylation, methylation and sumoylation. Additionally, limited proteolytic digestion of full-length STAT proteins (STATa) generates C-terminally truncated forms (STAT gamma) in different cell lineages, which have significantly reduced transcriptional activity due to the lack of the transactivation domain. Previously, it has been shown that STAT5 gamma, generated by an unidentified nuclear serine protease, plays an important role in myeloid cell differentiation and is aberrantly expressed in acute myeloid leukaemia. To better understand this regulatory mechanism for STAT5 function, we have purified the STAT5 protease from the immature myeloid cell line 32D and identified it by MS analysis as the granule-derived serine protease, CatG (cathepsin G). We show that purified CatG can specifically cleave full-length STAT5 to generate STAT5 gamma, and this activity can be inhibited by AEBSF [4-(2-aminoethyl)benzenesulfonyl fluoride] in an in vitro protease assay. Importantly, preparation of nuclear and cytoplasmic extracts from immature myeloid cell lines, 32D and FDC-P1, in the presence of a specific inhibitor for CatG results in the identification of STAT5 alpha only. These studies indicate that nuclear STAT5 gamma does not naturally exist in immature myeloid cells and is artificially generated from STAT5 alpha during the preparation of extracts due to the abundance of CatG in these cells. Therefore in contrast with earlier studies, our data suggest that STAT5 alpha, rather than STAT5 gamma is the active form in immature myeloid cells

AB - STAT (signal transducer and activator of transcription) proteins are critical regulators of cytokine-induced cell proliferation, differentiation and survival. STAT functional activity can be variably regulated by post-translational modifications, including phosphorylation, acetylation, methylation and sumoylation. Additionally, limited proteolytic digestion of full-length STAT proteins (STATa) generates C-terminally truncated forms (STAT gamma) in different cell lineages, which have significantly reduced transcriptional activity due to the lack of the transactivation domain. Previously, it has been shown that STAT5 gamma, generated by an unidentified nuclear serine protease, plays an important role in myeloid cell differentiation and is aberrantly expressed in acute myeloid leukaemia. To better understand this regulatory mechanism for STAT5 function, we have purified the STAT5 protease from the immature myeloid cell line 32D and identified it by MS analysis as the granule-derived serine protease, CatG (cathepsin G). We show that purified CatG can specifically cleave full-length STAT5 to generate STAT5 gamma, and this activity can be inhibited by AEBSF [4-(2-aminoethyl)benzenesulfonyl fluoride] in an in vitro protease assay. Importantly, preparation of nuclear and cytoplasmic extracts from immature myeloid cell lines, 32D and FDC-P1, in the presence of a specific inhibitor for CatG results in the identification of STAT5 alpha only. These studies indicate that nuclear STAT5 gamma does not naturally exist in immature myeloid cells and is artificially generated from STAT5 alpha during the preparation of extracts due to the abundance of CatG in these cells. Therefore in contrast with earlier studies, our data suggest that STAT5 alpha, rather than STAT5 gamma is the active form in immature myeloid cells

M3 - Article

VL - 404

SP - 81

EP - 87

JO - Biochemical Journal

JF - Biochemical Journal

IS - 1

ER -