Expression of BNIP3 in invasive breast cancer: correlations with the hypoxic response and clinicopathological features.
BACKGROUND
Bcl-2/adenovirus E1B 19 kDa-interacting protein 3 (BNIP3) is a pro-apoptotic member of the Bcl-2 family induced under hypoxia. Low or absent expression has recently been described in human tumors, including gastrointestinal tumors, resulting in poor prognosis. Little is known about BNIP3 expression in invasive breast cancer. The aim of the present study was to investigate the expression of BNIP3 in invasive breast cancer at the mRNA and protein level in correlation with the hypoxic response and clinicopathological features.


METHODS
In 40 cases of invasive breast cancer, BNIP3 mRNA in situ hybridization was performed on frozen sections with a digoxigenin labeled anti-BNIP3 probe. Paraffin embedded sections of the same specimens were used to determine protein expression of BNIP3, Hypoxia Inducible Factor 1 alpha (HIF-1alpha) and its downstream targets Glucose Transporter 1 (Glut-1) and Carbonic Anhydrase (CAIX) by immunohistochemistry.


RESULTS
BNIP3 mRNA was expressed in 16/40 (40%) of the cases and correlated with BNIP3 protein expression (p = 0.0218). Neither BNIP3 protein nor mRNA expression correlated with expression of HIF-1alpha expression or its downstream targets. Tumors which showed loss of expression of BNIP3 had significantly more often lymph node metastases (82% vs 39%, p = 0.010) and showed a higher mitotic activity index (p = 0.027). BNIP3 protein expression was often nuclear in normal breast, but cytoplasmic in tumor cells.


CONCLUSIONS
BNIP3 expression is lost in a significant portion of invasive breast cancers, which is correlated with poor prognostic features such as positive lymph node status and high proliferation, but not with the hypoxic response.
Koop
Esther A
EA
Department of Pathology, University Medical Center, Utrecht, The Netherlands. e.koop@gelre.nl
van Laar
Theo
T
van Wichen
Dick F
DF
de Weger
Roel A
RA
Wall
Elsken van der
Ev
van Diest
Paul J
PJ
D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000096:biosynthesis; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D051272:Glucose Transporter Type 1 / Q000096:biosynthesis; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis; D017403:In Situ Hybridization; D008207:Lymphatic Metastasis; D008565:Membrane Proteins / Q000096:biosynthesis*; D009361:Neoplasm Invasiveness; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism
C090121:BNIP3 protein, human; D051272:Glucose Transporter Type 1; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; C495677:SLC2A1 protein, human; D002256:Carbonic Anhydrases