On the role of thymopoietins in cell proliferation. Immunochemical evidence for new members of the human thymopoietin family

Thymopoietins (TMPOs) are a group of ubiquitously expressed nuclear protein s. They are suggested to play an important role in nuclear envelope organiz ation and cell cycle control, as has been shown for lamina-associated polyp eptides 2 alpha and beta, which are the rat homologs of human TMPO alpha an d TMPO beta, respectively. The recent isolation and characterization of sev en mouse TMPO mRNA transcripts named TMPO- alpha, beta, beta', gamma is an element of, delta, and zeta suggest that more than the three previously rep orted transcripts, alpha, beta, and gamma forms, may exist in humans. Here we report on the demonstration of putative human TMPO delta and is an eleme nt of by immunoblotting of human cell lines using a newly prepared polyclon al antiserum against the common N-terminal region of TMPO, Furthermore, we prepared the first truly TMPO beta-specific, affinity-purified polyclonal a ntiserum, using a part of the human analog of the beta-specific domain of m ouse TMPO 220-259 for immunization. We showed that human TMPO beta is highl y expressed in all cancerous cells tested, while hardly any cross-reactivit ies with other proteins could be detected. In contrast to the high expressi on of human TMPO beta in the cancer-derived neuroblastoma cell lines SK-N-M C and SMS-KAN, we found very low expression of human TMPO beta in low-proli ferative nerve tissue. These data led us to the assumption that expression of TMPO beta may correlate with the occurrence of cancer, and therefore may serve as a new tumor marker, or even as a new target for cancer therapy.