title: Modulation by Syk of Bcl-2, calcium and the calpain-calpastatin proteolytic system in human breast cancer cells.
abstract: Syk is a 72kDa non-receptor tyrosine kinase that is best characterized in hematopoietic cells. While Syk is pro-tumorigenic in some cancer cell types, it also has been reported as a negative regulator of metastatic cell growth in others. An examination of the RelA (p65) subunit of NF-κB expressed in MCF7 breast cancer cells indicated that either treatment with pervanadate or stable expression of Syk protected RelA from calpain-mediated proteolysis. Similar results were observed with the tyrosine phosphatase, PTP1B, another sensitive calpain substrate. The activity of calpain in MCF7 cell lysates was inhibited by both treatment with hydrogen peroxide and expression of Syk, the former due to oxidative inactivation of calpain and the latter to enhanced expression of calpastatin (CAST), the endogenous calpain inhibitor. The level of CAST was elevated in the cytosolic fraction of Syk-positive breast cancer cells resulting in more CAST present in complex with calpain in cell lysates. The high levels of CAST coincided with elevated basal levels of calcium-and of intracellular calpain activity-in Syk-expressing cells resulting from decreased levels of Bcl-2, an inhibitor of IP3-receptor-mediated calcium release. The inhibition of cellular calpain stimulated the Syk-mediated enhancement of NF-κB induced by TNF-α, enhanced tyrosine phosphorylation resulting from integrin crosslinking, and increased the localization of Syk to the plasma membrane.
authors.affiliation: Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Bei
authors.initials: B
authors.lastname: Fei
authors.forename: Shuai
authors.initials: S
authors.lastname: Yu
authors.forename: Robert L
authors.initials: RL
authors.lastname: Geahlen
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D002448:Cell Adhesion; D002465:Cell Movement; D049109:Cell Proliferation; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D016877:Oxidants / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013347:Subcellular Fractions; D000072377:Syk Kinase; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D002135:Calcium-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D016328:NF-kappa B; D016877:Oxidants; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; C033668:calpastatin; D006861:Hydrogen Peroxide; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D002154:Calpain; D002118:Calcium
keywords: Bcl-2; Calpain; Calpastatin; NF-κB; PTP1B; Syk