Homeobox transcription factor muscle segment homeobox 2 (Msx2) correlates with good prognosis in breast cancer patients and induces apoptosis in vitro.
BACKGROUND
The homeobox-containing transcription factor muscle segment homeobox 2 (Msx2) plays an important role in mammary gland development. However, the clinical implications of Msx2 expression in breast cancer are unclear. The aims of this study were to investigate the potential clinical value of Msx2 as a breast cancer biomarker and to clarify its functional role in vitro.


METHODS
Msx2 gene expression was first examined in a well-validated breast cancer transcriptomic dataset of 295 patients. Msx2 protein expression was then evaluated by immunohistochemistry in a tissue microarray (TMA) containing 281 invasive breast tumours. Finally, to assess the functional role of Msx2 in vitro, Msx2 was ectopically expressed in a highly invasive breast tumour cell line (MDA-MB-231) and an immortalised breast cell line (MCF10a), and these cell lines were examined for changes in growth rate, cell death and cell signalling.


RESULTS
Examination of Msx2 mRNA expression in a breast cancer transcriptomic dataset demonstrated that increased levels of Msx2 were associated with good prognosis (P = 0.011). Evaluation of Msx2 protein expression on a TMA revealed that Msx2 was detectable in both tumour cell nuclei and cytoplasm. Cytoplasmic Msx2 expression was associated with low grade tumours (P = 0.012) and Ki67 negativity (P = 0.018). Nuclear Msx2 correlated with low-grade tumours (P = 0.015), estrogen receptor positivity (P = 0.038), low Ki67 (P = 0.005) and high cyclin D1 expression (P = 0.037). Increased cytoplasmic Msx2 expression was associated with a prolonged breast cancer-specific survival (P = 0.049), recurrence-free survival (P = 0.029) and overall survival (P = 0.019). Ectopic expression of Msx2 in breast cell lines resulted in radically decreased cell viability mediated by induction of cell death via apoptosis. Further analysis of Msx2-expressing cells revealed increased levels of p21 and phosphorylated extracellular signal-regulated kinase (ERK) and decreased levels of Survivin and the 'split ends' (SPEN) protein family member RBM15.


CONCLUSIONS
We conclude that increased Msx2 expression results in improved outcome for breast cancer patients, possibly by increasing the likelihood of tumour cell death by apoptosis.
Lanigan
Fiona
F
University College Dublin School of Biomolecular and Biomedical Science, UCD Conway Institute, University College Dublin, Belfield, Dublin 4, Ireland.
Gremel
Gabriela
G
Hughes
Rowena
R
Brennan
Donal J
DJ
Martin
Finian
F
Jirström
Karin
K
Gallagher
William M
WM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D057809:HEK293 Cells; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry / Q000706:statistics & numerical data; D053208:Kaplan-Meier Estimate; D008875:Middle Aged; D011379:Prognosis; D016016:Proportional Hazards Models; D015398:Signal Transduction; D046888:Tissue Array Analysis
D018398:Homeodomain Proteins; C084119:MSX2 protein