Animal Cell Technology: Basic & Applied Aspects, Vol. 5, pp601-607, 1993.
Immunoglobulin Production Stimulating Factor (IPSF) Derived from Namalwa Cells.
Takuya Sugahara, Hiroto Nakajima, Sanetaka Shirahata, Ken-ichi Nagamine, and Hiroki Murakami
Two immunoglobulin production stimulating factors (IPSFs) were found in human Burkitt's lymphoma Namalwa cells. These IPSFs were IPSF-IIƒ¿ and IPSF-IIƒÀ, respectively. They enhanced IgM production of human-human and mouse-mouse hybridoma cells under serum-free conditions. IPSF-IIƒ¿ was purified from a Namalwa cell lysate and estimated to be a 112 kDa protein composed of one 40 kDa and two 36 kDa subunits. The active subunit of IPSF-IIƒ¿ (a 36 kDa peptide) was identified as glyceraldehyde-3-phosphate dehydrogenase (GPD; EC 126.96.36.199) on the basis of the N-terminal amino acid sequence and enzymic activity. As a result of evaluating the of IPSF activity of GPD, the enzyme showed as much IPSF activity as IPSF-IIƒ¿. The mode of action of GPD was then examined. Iodine-labeled GPD retained IPSF activity in spite of the complete loss of its enzymic activity. Therefore, the IPSF activity of this enzyme did not descend from its enzymic activity. Actinomycin D, a transcriptional inhibitor, could not suppress the enhancing effect of GPD on the antibody production of hybridomas. The enzyme stimulated the translation activity of a cell-free translation system made from HB4C5 cells. These results suggest that GPD stimulated monoclonal antibody production by enhancing the translation process of protein synthesis in hybridoma cells. IPSF-IIƒÀ was also purified and identified as enolase ƒ¿-chain (EC 188.8.131.52), an enzyme in the glycolytic pathway. The IPSF activity of enolase was not derived from its enzymic activity, like GPD. Moreover, inhibition of the transcription process in hybridoma cells with actinomycin D did not suppress the IPSF activity of enolase. As the result of an investigation on the mode of action of enolase, it seems that enolase stimulated monoclonal antibody production by the same mechanism as that for GPD.