PTMAP1

Recent animal studies demonstrate that prothymosin alpha 1 (ProT alpha) enhances the antitumor response by stimulation of mononuclear phagocyte functions. The present study was aimed at characterizing the in vitro effects by ProT alpha on blood monocytes from human colon cancer patients. Purified peripheral blood monocytes were studied in terms of tumor cytostatic ability and cytokine production after incubation with ProT alpha or interferon (rIFN-gamma) and transforming growth factor-beta (TGF beta), used as reference substances. SW620 colon carcinoma cells were used as tumor target cells in growth inhibition experiments. The level of baseline growth inhibitory activity of unstimulated patient's monocytes was significantly lower than that of normal monocytes. The defective antitumor activity of patient monocytes was associated with a higher production of the inhibitory monokines prostaglandin E2 (PGE2) and TGF beta. The stimulation of monocytes by ProT alpha and/or rIFN-gamma elevated the average antitumor activity in all donor groups. The ProT alpha-induced increase was associated with a significantly higher monocytic secretion of IL-1 beta and TNF-alpha. Moreover, the concentrations of TGF beta and PGE2 in the culture supernatants decreased significantly, when patient's monocytes were treated with ProT alpha and/or rIFN-gamma. Additionally, ProT alpha enhanced the diminished antitumor activity of TGF beta-treated normal monocytes. These results suggest that ProT alpha selectively regulates distinct functions of blood monocytes, the effect of this cytokine varying with the parameter and donor population examined. These data provide a rational and biological endpoint for further studies with ProT alpha as an activator of mononuclear function in colon cancer.

The six members of the human prothymosin alpha gene family have been cloned and sequenced. One gene (PTMA) contains introns and appears to be the source of all isolated prothymosin alpha cDNAs. The remaining five genes are processed pseudogenes. Four of them have consensus TATA elements upstream of sequences nearly identical to the transcriptional start region of the intron-containing gene. Those four genes also contain open reading frames coding for proteins closely related to prothymosin alpha. In two of the pseudogenes, PTMAP2 and 5, the encoded proteins differ from the product of the parental gene at only two and four locations, respectively. The fifth pseudogene (PTMAP1) encodes a different protein owing to an upstream translational initiation start site and multiple deletions and insertions. Because the potential for expression exists in this system, a search for pseudogenomic transcripts was undertaken using the polymerase chain reaction to amplify reverse transcripts of mRNAs from many human tissues and bulk DNA from several human cDNA libraries. Evidence for pseudogenomic transcripts was not obtained. Therefore, we conclude that the human prothymosin alpha gene family contains only one functional gene.

Recently we demonstrated that, in vitro, prothymosin alpha 1 (ProT alpha), a polypeptide from calf thymus, was able to enhance the deranged tumoristatic activity of peripheral blood monocytes from melanoma patients. Now we report, that the thymic preparation Thymex-L significantly enhanced the level of depressed monocyte activity from 19% to 26%, whereas in normal donor groups no significant change of basal activity (35%) was seen. Although the improvement of median levels of killer cell activity was found to be independent from the disease stage, the Thymex-L effect was only statistically significant in stage I and melanoma patients after chemotherapy. In contrast to ProT alpha, Thymex-L did not further enhance monocyte-mediated cytotoxicity when it was applied in combination with rIFN-gamma. However, after stimulation with rIFN-gamma, the median level of TNF-alpha secretion by melanoma monocytes significantly increased (about 2-fold) when preincubated with Thymex-L. These results indicate that depressed monocyte functions in selected melanoma patients may be partially improved by Thymex-L.