Production of thrombopoietin by human carcinomas and its novel isoforms.
Thrombocytosis is occasionally seen in patients with carcinomas and has been assumed to be attributable to interleukin-6 or granulocyte-macrophage colony-stimulating factor produced by carcinoma cells. In this study, we clarified whether thrombopoietin (TPO) is involved in carcinoma-associated thrombocytosis. Expression of TPO mRNA was observed in the majority of 27 carcinoma cell lines as determined by reverse transcriptase-polymerase chain reaction (RT-PCR). There were 6 PCR products differing in size; sequence analysis showed the full-length TPO mRNA (TPO-1), 12- and 116-bp deleted variants (TPO-2 and TPO-3, respectively), and 3 novel isoforms (197- and 128-bp deleted forms and a 60-bp insert form of TPO-3; named TPO-4, TPO-5, and TPO-6, respectively). Of 27 lines, 24 expressed TPO-1 mRNA with various other isoforms. Culture supernatants of COS-1 cells transfected with TPO-5 or TPO-6 cDNA did not promote the proliferation of TPO-responsive cells, whereas Western blot analysis on the cell lysates demonstrated TPO-5 but not TPO-6 protein, suggesting poor extracellular secretion (TPO-5) or poor protein synthesis (TPO-6). TPO protein was detected in 10-fold concentrated culture supernatants of cells of these carcinoma lines, with a median concentration of 0.38 fmol/mL as evaluated by enzyme-linked immunosorbent assay. High blood TPO levels were observed with a median value of 3.46 fmol/mL (range, 0.34 to 8.67 fmol/mL) in patients with advanced carcinomas associated with thrombocytosis. These results indicate that thrombocytosis in patients with carcinomas might be caused, at least in part, by TPO produced by carcinoma cells.
Sasaki
Y
Y
Department of Medicine and Clinical Science, Kyoto University Graduate School of Medicine, Kyoto, Japan.
Takahashi
T
T
Miyazaki
H
H
Matsumoto
A
A
Kato
T
T
Nakamura
K
K
Iho
S
S
Okuno
Y
Y
Nakao
K
K
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D004251:DNA Transposable Elements; D005260:Female; D014644:Genetic Variation; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017384:Sequence Deletion; D013926:Thrombopoietin / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D004251:DNA Transposable Elements; D020033:Protein Isoforms; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013926:Thrombopoietin