Mammary derived growth inhibitor is not a distinct protein but a mix of heart-type and adipocyte-type fatty acid-binding protein.
The amino acid sequence of the mammary derived growth inhibitor (MDGI) from bovine mammary gland (Böhmer, F.-D., Kraft, R., Otto, A. , Wernstedt, C., Hellman, U., Kurtz, A., Müller, T., Rohde, K., Etzold, G., Lehmann, W., Langen, P., Heldin, C.-H., and Grosse, R. (1987) J. Biol. Chem. 262, 15137-15143) revealed 95% identity to bovine heart fatty acid-binding protein (H-FABP), explaining the observed immunocross-reactivity. However, a cDNA encoding MDGI has not been found to date. Artificial MDGI cDNA was expressed in an in vitro transcription/translation assay. Analysis by isoelectric focusing of the immunoprecipitated in vitro translation products of lactating bovine mammary gland mRNA did not indicate a protein corresponding to the in vitro translation product of artificial MDGI mRNA. Moreover, two-dimensional electrophoresis of bovine mammary gland proteins confirmed the absence of a protein with the pI of the in vitro translated artificial MDGI mRNA in bovine mammary gland and instead revealed, apart from H-FABP, an unknown protein that was recognized by anti-H-FABP antibodies. From lactating bovine mammary gland the cDNA for adipocyte fatty acid-binding protein (A-FABP) was cloned. The in vitro translation of recombinant mRNA derived from this cDNA yielded a polypeptide that behaved like the unknown immunoreactive protein. Western blotting and immunofluorescence using monospecific antibodies demonstrated the coexistence of H-FABP and A-FABP in the lactating mammary gland. Taking into account that deviations of the MDGI sequence from the bovine H-FABP sequence correspond with A-FABP we attribute the structure originally reported as MDGI to a mix of these proteins.
Specht
B
B
Department of Biochemistry, University of Münster, D-48149 Münster, Germany.
Bartetzko
N
N
Hohoff
C
C
Kuhl
H
H
Franke
R
R
Börchers
T
T
Spener
F
F
D000273:Adipose Tissue / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D017931:DNA Primers / Q000737:chemistry; D015180:Electrophoresis, Gel, Two-Dimensional; D000074026:Fatty Acid Binding Protein 3; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D006801:Humans; D007526:Isoelectric Point; D008321:Mammary Glands, Animal / Q000737:chemistry*; D051379:Mice; D008969:Molecular Sequence Data; D018996:Myelin P2 Protein / Q000737:chemistry* / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger / Q000235:genetics; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; D017931:DNA Primers; C493408:FABP3 protein, human; C107608:FABP7 protein, human; C493409:Fabp3 protein, mouse; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; D000074026:Fatty Acid Binding Protein 3; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D025521:Tumor Suppressor Proteins