Role of KCNMA1 gene in breast cancer invasion and metastasis to brain.
BACKGROUND
The prognosis for patients with breast tumor metastases to brain is extremely poor. Identification of prognostic molecular markers of the metastatic process is critical for designing therapeutic modalities for reducing the occurrence of metastasis. Although ubiquitously present in most human organs, large-conductance calcium- and voltage-activated potassium channel (BKCa) channels are significantly upregulated in breast cancer cells. In this study we investigated the role of KCNMA1 gene that encodes for the pore-forming alpha-subunit of BKCa channels in breast cancer metastasis and invasion.


METHODS
We performed Global exon array to study the expression of KCNMA1 in metastatic breast cancer to brain, compared its expression in primary breast cancer and breast cancers metastatic to other organs, and validated the findings by RT-PCR. Immunohistochemistry was performed to study the expression and localization of BKCa channel protein in primary and metastatic breast cancer tissues and breast cancer cell lines. We performed matrigel invasion, transendothelial migration and membrane potential assays in established lines of normal breast cells (MCF-10A), non-metastatic breast cancer (MCF-7), non-brain metastatic breast cancer cells (MDA-MB-231), and brain-specific metastatic breast cancer cells (MDA-MB-361) to study whether BKCa channel inhibition attenuates breast tumor invasion and metastasis using KCNMA1 knockdown with siRNA and biochemical inhibition with Iberiotoxin (IBTX).


RESULTS
The Global exon array and RT-PCR showed higher KCNMA1 expression in metastatic breast cancer in brain compared to metastatic breast cancers in other organs. Our results clearly show that metastatic breast cancer cells exhibit increased BKCa channel activity, leading to greater invasiveness and transendothelial migration, both of which could be attenuated by blocking KCNMA1.


CONCLUSIONS
Determining the relative abundance of BKCa channel expression in breast cancer metastatic to brain and the mechanism of its action in brain metastasis will provide a unique opportunity to identify and differentiate between low grade breast tumors that are at high risk for metastasis from those at low risk for metastasis. This distinction would in turn allow for the appropriate and efficient application of effective treatments while sparing patients with low risk for metastasis from the toxic side effects of chemotherapy.
Khaitan
Divya
D
Department of Laboratory Oncology Research, Curtis and Elizabeth Anderson Cancer Institute, Hoskins Center for Biomedical Research, Savannah, Georgia 31404, USA. divyakh@rediffmail.com
Sankpal
Umesh T
UT
Weksler
Babette
B
Meister
Edward A
EA
Romero
Ignacio A
IA
Couraud
Pierre-Olivier
PO
Ningaraj
Nagendra S
NS
D001932:Brain Neoplasms / Q000235:genetics / Q000378:metabolism / Q000556:secondary*; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D002462:Cell Membrane / Q000378:metabolism; D002465:Cell Movement; D005091:Exons; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics* / Q000502:physiology*; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D010455:Peptides / Q000494:pharmacology; D011379:Prognosis; D034741:RNA, Small Interfering / Q000378:metabolism
C494841:KCNMA1 protein, human; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D010455:Peptides; D034741:RNA, Small Interfering; C064719:iberiotoxin