Increasing CD44+/CD24(-) tumor stem cells, and upregulation of COX-2 and HDAC6, as major functions of HER2 in breast tumorigenesis.
BACKGROUND
Cancer cells are believed to arise primarily from stem cells. CD44+/CD24(-) have been identified as markers for human breast cancer stem cells. Although, HER2 is a well known breast cancer oncogene, the mechanisms of action of this gene are not completely understood. Previously, we have derived immortal (M13SV1), weakly tumorigenic (M13SV1R2) and highly tumorigenic (M13SV1R2N1) cell lines from a breast epithelial cell type with stem cell phenotypes after successive SV40 large T-antigen transfection, X-ray irradiation and ectopic expression of HER2/C-erbB2/neu. Recently, we found that M13SV1R2 cells became non-tumorigenic after growing in a growth factor/hormone-deprived medium (R2d cells).


RESULTS
In this study, we developed M13SV1R2N1 under the same growth factor/hormone-deprived condition (R2N1d cells). This provides an opportunity to analyze HER2 effect on gene expression associated with tumorigenesis by comparative study of R2d and R2N1d cells with homogeneous genetic background except HER2 expression. The results reveal distinct characters of R2N1d cells that can be ascribed to HER2: 1) development of fast-growing tumors; 2) high frequency of CD44+/CD24(-) cells (~50% for R2N1d vs. ~10% for R2d); 3) enhanced expression of COX-2, HDAC6 mediated, respectively, by MAPK and PI3K/Akt pathways, and many genes associated with inflammation, metastasis, and angiogenesis. Furthermore, HER2 expression can be down regulated in non-adhering R2N1d cells. These cells showed longer latent period and lower rate of tumor development compared with adhering cells.


CONCLUSIONS
HER2 may induce breast cancer by increasing the frequency of tumor stem cells and upregulating the expression of COX-2 and HDAC6 that play pivotal roles in tumor progression.
Graduate Institute of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
Kai-Hung
KH
Wang
An-Pei
AP
Kao
Chia-Cheng
CC
Chang
Jau-Nan
JN
Lee
Ming-Feng
MF
Hou
Cheng-Yu
CY
Long
Hung-Sheng
HS
Chen
Eing-Mei
EM
Tsai
D000818:Animals; D015153:Blotting, Western; D051927:CD24 Antigen / Q000378:metabolism*; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005434:Flow Cytometry; D000073864:Histone Deacetylase 6; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D016513:Mice, SCID; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology
D051927:CD24 Antigen; D051546:Cyclooxygenase 2; D000073864:Histone Deacetylase 6; D006655:Histone Deacetylases; D018960:Hyaluronan Receptors; D018719:Erb-b2 Receptor Tyrosine Kinases; C496540:PTGS2 protein, human; C433811:HDAC6 protein, human