KLF4α stimulates breast cancer cell proliferation by acting as a KLF4 antagonist.
Krüppel-like factor 4 (KLF4), a transcription factor involved in both tumor suppression and oncogenesis in various human tumors, is subject to alternative splicing that produces KLF4α. KLF4α is primarily expressed in the cytoplasm because it lacks exon 3 of KLF4, which contains the nuclear localization signal. The role of KLF4 in breast cancer remains unclear and nothing is known yet about the expression and function of the isoform KLF4α. Here, we show that KLF4α is expressed in normal and tumoral tissue of the breast and provide evidence that the KLF4α/KLF4(full-length) (FL) ratio is increased in tumors compared to corresponding normal tissue. Forced increase of the KLF4α/KLF4(FL) ratio in the metastatic breast cancer cell line MDA-MB-231 decreases the levels of E-Cadherin, p21Cip1, and p27Kip1, three known KLF4(FL) target genes, and stimulates cell proliferation. We suggest that cytoplasmic KLF4α binds to KLF4(FL) and retains it in the cytoplasm thereby antagonizing the gene regulatory activities of KLF4(FL) in the nucleus. Our results establish KLF4α as a KLF4 isoform that opposes the function of KLF4(FL) and as an important factor in the complex and unresolved role of KLF4(FL) in breast carcinogenesis.
Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Basel, Switzerland.
Jacqueline
J
Ferralli
Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Basel, Switzerland.|Faculty of Science, University of Basel, Basel, Switzerland.
Ruth
R
Chiquet-Ehrismann
Friedrich Miescher Institute for Biomedical Research, Novartis Research Foundation, Basel, Switzerland.|Department of Orthodontics and Dentofacial Orthopedics, School of Dental Medicine, University of Bern, Bern, Switzerland.
Martin
M
Degen
D017398:Alternative Splicing; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000502:physiology*; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D005260:Female; D006801:Humans; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism*
C000715467:KLF4 protein, human; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D020033:Protein Isoforms
KLF4; KLF4α/KLF4(FL) ratio; alternative splicing; proliferation; tumors