High expression of a cytokeratin-associated protein in many cancers.
We have described previously a cDNA library made from membrane-bound polysomal mRNA prepared from breast and prostate cancer cell lines. The library is highly enriched for cDNAs encoding membrane proteins, secreted proteins, and cytokeratins. To characterize this library, 25,277 cDNA clones were sequenced and aligned with various databases; 1,439 clones did not align with known genes. From this set of clones we identified a previously uncharacterized gene encoding a 334-aa protein. Although protein structural motif prediction programs indicate that the gene encodes a membrane protein comprising a signal sequence, a series of leucine-rich repeats, and a single transmembrane domain with a cytoplasmic tail, confocal microscopy of MCF7 breast cancer cells demonstrates that the protein is not directly associated with the plasma membrane or intracellular membranes but instead colocalizes with intermediate filaments and cytokeratins within the cell. Immunofluorescence studies also show that protein expression is increased greatly in mitotic MCF7 cells, and immunohistochemistry demonstrates its expression in human breast cancer cells. Analysis of mRNA levels in 25 different normal tissues by RT-PCR shows that this gene is expressed highly in normal prostate and salivary gland, very weakly in colon, pancreas, and intestine, and not at all in other tissues. RT-PCR studies on human cancer samples show that the RNA is expressed highly in many cancer cell lines and cancer specimens, including 26 of 33 human breast cancers, 3 of 3 prostate cancers, 3 of 3 colon cancers, and 3 of 3 pancreatic cancers. We name the protein CAPC, cytokeratin-associated protein in cancer.
South Dakota Health Research Foundation-Signal Transduction Institute, University of South Dakota School of Medicine and Sioux Valley Hospitals and Health System, Sioux Falls, SD 57105, USA.
Kristi A
KA
Egland
Xiu Fen
XF
Liu
Stephen
S
Squires
Satoshi
S
Nagata
Yan-Gao
YG
Man
Tapan K
TK
Bera
Masanori
M
Onda
James J
JJ
Vincent
Robert L
RL
Strausberg
Byungkook
B
Lee
Ira
I
Pastan
D000595:Amino Acid Sequence; D001943:Breast Neoplasms / Q000235:genetics; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D005260:Female; D015723:Gene Library; D006801:Humans; D007633:Keratins / Q000235:genetics*; D008297:Male; D008938:Mitosis; D008969:Molecular Sequence Data; D009369:Neoplasms / Q000235:genetics*; D016366:Open Reading Frames; D011471:Prostatic Neoplasms / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D012333:RNA, Messenger; D007633:Keratins