Overexpression of ecto-protein kinases in prostasomes of metastatic cell origin.
BACKGROUND
Prostasomes are secretory granules produced, stored, and released by the glandular epithelial cells of the prostate. They express numerous enzymes whose physiological roles have so far not been fully evaluated. In this study, we investigated the expression and function of prostasomal protein kinases and ATPase.


METHODS
The protein kinase activities of prostasomes isolated from seminal fluid and malignant prostate cell lines (PC-3, DU145, and LNCaP) were investigated using the model phosphorylation substrates histone and casein, as well as the plasma proteins C3 and fibrinogen, in combination with specific protein kinase inhibitors. The prostasomal ATPase activity was also evaluated. The expression of protein kinases and ATPase on prostasomes was verified by flow cytometry.


RESULTS
Prostasomes (intact or solubilized with octylglucoside or saponin) from prostate cancer cells had higher expression of protein kinases A, C, and casein kinase II compared to prostasomes isolated from seminal plasma, resulting in higher phosphorylation of both exogenous and endogenous substrates. Using intact prostasomes, it was found that prostasomes of metastatic origin had lower ATPase activity, resulting in higher residual ATP available for the phosphorylation reaction. Finally, complement component C3 and fibrinogen (two proteins whose activities are modulated by phosphorylation) were identified as physiologically relevant phosphorylation substrates.


CONCLUSIONS
These results indicate that prostasomes are capable of modifying proteins possibly involved in the innate response by extracellular phosphorylation mediated by ecto-kinases. This is a novel mechanism by which prostatic malignant cells may interact with their environment.
Babiker
Adil A
AA
Department of Oncology, Radiology, and Clinical Immunology, Division of Clinical Immunology, Rudbeck Laboratory C5, Uppsala, Sweden.
Ronquist
Gunnar
G
Nilsson
Bo
B
Ekdahl
Kristina Nilsson
KN
D000251:Adenosine Triphosphatases / Q000096:biosynthesis* / Q000378:metabolism; D020869:Gene Expression Profiling; D006801:Humans; D008297:Male; D009362:Neoplasm Metastasis / Q000235:genetics*; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000235:genetics* / Q000473:pathology*; D011494:Protein Kinases / Q000096:biosynthesis* / Q000378:metabolism; D022142:Secretory Vesicles / Q000201:enzymology*; D014407:Tumor Cells, Cultured
D011494:Protein Kinases; D000251:Adenosine Triphosphatases