Stable amino-acid sequence of the mannose-6-phosphate/insulin-like growth-factor-II receptor in ovarian carcinomas with loss of heterozygosity and in breast-cancer cell lines.
The mannose-6-phosphate/insulin-like growth factor 2 receptor (Man-6-P/IGFII receptor) is involved in lysosomal enzyme sorting, IGFII degradation and pro-TGFbeta activation. Genetic alterations in hepatocarcinomas and a few breast cancers suggest that this receptor behaves as a tumor suppressor. Moreover, hypersecretion and Man-6-P-independent targeting of cathepsins in breast and ovarian carcinomas also suggest alterations in this receptor. We studied the Man-6-P/IGFII receptor gene in 8 ovarian carcinomas, and 4 breast- and ovarian-cancer cell lines. The results confirmed a frequent loss of heterozygosity (LOH) in the 6q27-qter region in 5 out of 8 ovarian carcinomas. We used 23 overlapping RT-PCR fragments to sequence the whole coding region of the Man-6-P/IGFII receptor. The 2491 amino-acid sequence of this receptor was perfectly conserved in 9 out of 10 of our samples, including MCF7 and MDA-MB231 cells and 5 ovarian carcinomas with LOH. This allowed us to rectify the 2 previously published sequences which differed in several bases, and to propose a consensus amino-acid sequence. The only amino-acid change (Thr --> Ala) was in BG1 ovarian-cancer cells, and was due to an A-to-G substitution on one allele at nucleotide 2561. We found no bi-allelic alterations in the 9 ovarian carcinomas, but 3 silent nucleotide substitutions leading to a lower cordon usage in 2 ovarian carcinomas with LOH. No mutation of the Man-6-P/IGFII receptor coding sequence was found in breast-cancer cell lines to explain the cathepsin-D hypersecretion and Man-6-P-independent trafficking described. We propose that, in breast and ovarian cancers, the frequent loss of one allele, associated with over-expression of some of its ligands, might be sufficient to saturate the receptor protein, displace the ligands to other sites, and consequently facilitate tumor progression.
Rey
J M
JM
Laboratoire de Biologie Cellulaire et Hormonale, CHRU Arnaud de Villeneuve, Montpellier, France.
Theillet
C
C
Brouillet
J P
JP
Rochefort
H
H
D000328:Adult; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001483:Base Sequence; D001943:Breast Neoplasms / Q000473:pathology*; D002874:Chromosome Mapping; D002896:Chromosomes, Human, Pair 6; D016384:Consensus Sequence; D017124:Conserved Sequence; D017931:DNA Primers; D004273:DNA, Neoplasm / Q000737:chemistry; D005260:Female; D006801:Humans; D019656:Loss of Heterozygosity; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000235:genetics* / Q000473:pathology*; D017527:Receptor, IGF Type 2 / Q000737:chemistry* / Q000235:genetics*; D012091:Repetitive Sequences, Nucleic Acid; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D004273:DNA, Neoplasm; D017527:Receptor, IGF Type 2