Murine hybridoma/plasmacytoma growth factor. Complete amino-acid sequence and relation to human interleukin-6.

Murine interleukin-HP1 (HP1) was originally identified as a T-cell-derived lymphokine with growth factor activity for B-cell hybridomas and plasmacytomas. This growth factor was recently shown to stimulate both normal B-cell differentiation and T-cell growth factor activity. We have determined the complete amino acid sequence of HP1 on 40 micrograms (approximately 2 nmol) protein using a combination of sensitive microbore column (1.0 and 2.1 mm internal diameter) HPLC, peptide mapping and automated amino acid microsequence analysis. Ion-pairing chromatography was employed to isolate hydrophilic peptides which were not retained on conventional reversed-phase HPLC systems. The molecule consists of 187 amino acid residues with a calculated molecular mass of 21710 Da. Although there is virtually no similarity between the NH2-terminal region of HP1 and its human biological counterpart (26-kDa protein/interferon-beta 2 = B-cell stimulatory factor-2/interleukin-6), these studies demonstrate extensive amino acid similarity in the middle and COOH-terminal regions of these molecules suggesting that HP1 is the murine homologue of human interleukin-6.