Downregulation of SIAH2, an ubiquitin E3 ligase, is associated with resistance to endocrine therapy in breast cancer.
OBJECTIVE
In our microarray analysis we observed that Seven-in-Absentia Homolog 2 (SIAH2) levels were low in estrogen receptor (ER) positive breast tumors of patients resistant to first-line tamoxifen therapy. The aim of this study was to evaluate SIAH2 for its (a) predictive/prognostic value, and (b) functional role in endocrine therapy resistance.


METHODS
SIAH2 expression was measured with quantitative Real-Time-PCR (qRT-PCR) in 1205 primary breast tumor specimens and related to disease outcome. The functional role of SIAH2 was determined in human breast cancer cell lines ZR-75-1, ZR/HERc, and MCF7. Cell lines were treated with estrogen (E2), anti-estrogen ICI164.384 or epidermal growth factor (EGF). Moreover, MCF7 was treated with ICI164.384 after silencing SIAH2 expression.


RESULTS
SIAH2 was not prognostic in 603 lymph node negative patients who had not received adjuvant systemic therapy. In multivariate analysis of ER-positive tumors of 235 patients with recurrent disease, SIAH2 as continuous variable, significantly predicted first-line tamoxifen treatment failure (OR = 1.48; P = 0.05) and progression-free survival (PFS) (HR = 0.79; P = 0.007). Furthermore, in primary breast cancer patients treated with adjuvant tamoxifen, SIAH2 predicted metastasis-free survival (MFS) (HR = 0.73; P = 0.005). In vitro experiments showed that SIAH2 silencing in MCF7 cells resulted in resistance to ICI164.384-treatment when compared with mock silenced cells (P = 0.008). Interestingly, in ZR cells transfected with EGFR (ZR/HERc), SIAH2 expression was induced by E2 but downregulated by EGF.


CONCLUSIONS
In primary breast tumor specimens as well as in vitro low SIAH2 levels associated with resistance to endocrine therapy. Moreover, SIAH2 expression showed an opposite regulation by E2 and EGF.
Jansen
Maurice P H M
MP
Department of Medical Oncology, Erasmus MC, Josephine Nefkens Institute, Rotterdam, The Netherlands. m.p.h.m.jansen@erasmusmc.nl
Ruigrok-Ritstier
Kirsten
K
Dorssers
Lambert C J
LC
van Staveren
Iris L
IL
Look
Maxime P
MP
Meijer-van Gelder
Marion E
ME
Sieuwerts
Anieta M
AM
Helleman
Jozien
J
Sleijfer
Stefan
S
Klijn
Jan G M
JG
Foekens
John A
JA
Berns
Els M J J
EM
D000328:Adult; D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D014408:Biomarkers, Tumor / Q000235:genetics*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D018572:Disease-Free Survival; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008875:Middle Aged; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011379:Prognosis; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020845:Selective Estrogen Receptor Modulators / Q000627:therapeutic use; D016896:Treatment Outcome; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism; D000098563:Seven in Absentia Proteins
D018931:Antineoplastic Agents, Hormonal; D014408:Biomarkers, Tumor; D009687:Nuclear Proteins; D012333:RNA, Messenger; D020845:Selective Estrogen Receptor Modulators; D004958:Estradiol; D004815:Epidermal Growth Factor; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D066246:ErbB Receptors