High-level expression of TGF-beta 2 and the TGF-beta 2(414) precursor in Chinese hamster ovary cells

Chinese hamster ovary (CHO) clones secreting high levels of transforming growth factor-beta 2 (TGF-beta 2) were obtained after transfection with a cDNA clone coding for the 414-amino acid TGF-beta 2 precursor and subsequent amplification with methotrexate. The TGF-beta 2 was secreted in a latent form since acidification was necessary for detection of maximal levels of bioactivity. Amino- and carboxy-terminal sequencing of purified recombinant TGF-beta 2 indicated that correct processing of mature TGF-beta 2 had occurred. In addition to mature TGF-beta 2, the recombinant CHO clones secreted larger proteins having molecular weights of 85, 105, and 130 kD, which consisted of both mature and pro-region sequences when analyzed by immunoblotting using site-specific anti-peptide antibodies. Analysis of serum- and cell-free media from recombinant CHO cells metabolically labeled with [3H]glucosamine and [32P]orthophosphate indicated that pro-TGF-beta 2 was glycosylated and phosphorylated. Two-dimensional electrophoretic analysis of acid hydrolysates showed that the 32P was incorporated into mannose-6-phosphate.