GROalpha is highly expressed in adenocarcinoma of the colon and down-regulates fibulin-1.
OBJECTIVE
The growth-related oncogene alpha (GROalpha) is a secreted interleukin-like molecule that interacts with the CXCR2 G-protein-coupled receptor. We found that the mRNA and protein products of GROalpha are more highly expressed in neoplastic than normal colon epithelium, and we studied potential mechanisms by which GROalpha may contribute to tumor initiation or growth.


METHODS
Cell lines that constitutively overexpress GROalpha were tested for growth rate, focus formation, and tumor formation in a xenograft model. GROalpha expression was determined by Affymetrix GeneChip (241 microdissected colon samples), real-time PCR (n = 32), and immunohistochemistry. Primary colon cancer samples were also employed to determine copy number changes and loss of heterozygosity related to the GROalpha and fibulin-1 genes.


RESULTS
In cell cultures, GROalpha transfection transformed NIH 3T3 cells, whereas inhibition of GROalpha by inhibitory RNA was associated with apoptosis, decreased growth rate, and marked up-regulation of the matrix protein fibulin-1. Forced expression of GROalpha was associated with decreased expression of fibulin-1. Expression of GROalpha mRNA was higher in primary adenocarcinomas (n = 132), adenomas (n = 32), and metastases (n = 52) than in normal colon epithelium (P < 0.001). These results were confirmed by real-time PCR and by immunohistochemistry. Samples of primary and metastatic colon cancer showed underexpression of fibulin-1 when compared with normal samples. There were no consistent changes in gene copy number of GROalpha or fibulin-1, implying a transcriptional basis for these findings.


CONCLUSIONS
Elevated expression of GROalpha is frequent in adenocarcinoma of the colon and is associated with down-regulation of the matrix protein fibulin-1 in experimental models and in clinical samples. GROalpha overexpression abrogates contact inhibition in cell culture models, whereas inhibition of GROalpha expression is associated with apoptosis. Importantly, coexpression of fibulin-1 with GROalpha abrogates key aspects of the transformed phenotype, including tumor formation in a murine xenograft model. Targeting GRO proteins may provide new opportunities for treatment of colon cancer.
Wen
Yu
Y
Robert Wood Johnson Medical School and Cancer Institute of New Jersey, New Brunswick, New Jersey 08903, USA.
Giardina
Sarah F
SF
Hamming
David
D
Greenman
Jennifer
J
Zachariah
Emmanuel
E
Bacolod
Manny D
MD
Liu
Hao
H
Shia
Jinru
J
Amenta
Peter S
PS
Barany
Francis
F
Paty
Phillip
P
Gerald
William
W
Notterman
Daniel
D
D016475:3T3 Cells; D000230:Adenocarcinoma / Q000235:genetics* / Q000473:pathology; D000818:Animals; D002135:Calcium-Binding Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D002470:Cell Survival; D054360:Chemokine CXCL1; D019743:Chemokines, CXC / Q000235:genetics*; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology; D004273:DNA, Neoplasm / Q000235:genetics; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics*; D051379:Mice; D009368:Neoplasm Transplantation; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D014183:Transplantation, Heterologous
C475829:CXCL1 protein, human; D002135:Calcium-Binding Proteins; D054360:Chemokine CXCL1; D019743:Chemokines, CXC; D004273:DNA, Neoplasm; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; C060820:fibulin