A splice variant of CD99 increases motility and MMP-9 expression of human breast cancer cells through the AKT-, ERK-, and JNK-dependent AP-1 activation signaling pathways.
The CD99 gene encodes two distinct transmembrane proteins by alternative splicing of its transcript. To examine the effects of two CD99 isoforms on the invasive phenotypes of breast cancer cells, MDA-MB-231 and MCF-7 human breast cancer cell lines were stably transfected with CD99 cDNAs encoding the major wild-type form (type I) or a minor splice variant (type II). As a result, expression of CD99 type II, but not type I, markedly elevated the motility, binding to fibronectin, MMP-9 expression, and invasiveness of MDA-MB-231 and MCF-7 breast cancer cells. In MDA-MB-435 breast cancer cells expressing both CD99 type I and type II, invasion-related cellular activities were inhibited by the transfection of small interfering RNA (siRNA) targeted to CD99 type II. Meanwhile, CD99 type II-induced MMP-9 expression in MDA-MB-231 cells was shown to be mediated by the binding of AP-1 factors to the MMP-9 gene promoter. Gel shift assay revealed that ligation of CD99 type II with antibody resulted in the binding of JunD to the AP-1 site of the MMP-9 promoter region. Initiation of CD99 type II signaling by antibody ligation increased expression of JunD and FosB AP-1 factors, along with phosphorylation of Src, Akt, p38 MAPK, ERK, and JNK. Knockdown of JunD and FosB by siRNA transfection abolished the positive effects of CD99 type II on the motility and MMP-9 expression of MDA-MB-231 cells. Increased expression of JunD and FosB as well as elevated cell motility and MMP-9 expression by CD99 type II ligation were also abrogated by inhibitors, dominant-negative forms, and siRNAs for Akt1, ERK1/2, and JNK1 but not for p38 MAPK. These results suggest that expression of a splice variant of CD99 contributes to the invasive ability of human breast cancer cells by up-regulating AP-1-mediated gene expression through the Akt-dependent ERK and JNK signaling pathways.
Byun
Hee-Jung
HJ
Vascular System Research Center and Division of Life Sciences, College of Natural Sciences, Department of Anatomy, Kangwon University, South Korea.
Hong
In-Kee
IK
Kim
Eunsook
E
Jin
Young-June
YJ
Jeoung
Doo-Il
DI
Hahn
Jang-Hee
JH
Kim
Young-Myoung
YM
Park
Seong Hoe
SH
Lee
Hansoo
H
D000071443:12E7 Antigen; D017398:Alternative Splicing; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002465:Cell Movement; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*
D000071443:12E7 Antigen; D015703:Antigens, CD; C061828:CD99 protein, human; D015815:Cell Adhesion Molecules; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D018808:Transcription Factor AP-1; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020780:Matrix Metalloproteinase 9