THP-1, a human myeloid leukemia cell line, which secretes activin-A after phorbol ester induced cell differentiation, was used to examine the possible expression and presence of activin receptors because activin, a member of the transforming growth factor beta (TGF-beta) superfamily, has been found to be up-regulated by phorbol ester. We have studied whether THP-1 cells transcribe mRNAs encoding for activin receptors II and IIB by the reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization techniques. To confirm that THP-1 cells produce activin-A, we also determined the presence of immunoreactivity for activin-A by immunocytochemistry. We observed that messenger RNA encoding activin beta A-subunit was also expressed in THP-1 cells. Furthermore, the identity of RT-PCR products was confirmed by DNA sequencing. These results indicate that activin-A and its receptors are co-expressed in THP-1 cells and suggest that activin-A may have autocrine functions during cell proliferation in these cells.

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