Transcription factor OCT1 regulates adult and malignant stem cells

For many years the Oct1 transcription factor was though to behave as a static regulator of housekeeping genes and was constitutively bound to the octamer binding sites of its targets. However, recently there has been a significant amount of evidence from our lab and others that has shifted the paradigm and caused the scientific community to change the way they think about this transcription factor. Oct4, a close family member to Oct1, is well known to be a regulator of pluripotency in embryonic stem cells. Oct4 and Oct1 have similar binding site specificity, similar gene targets and they are both observed to display stem cell properties. However, the role of Oct1 in stem cell identity was unknown. I have established that Oct1 is dynamically regulated and critical for somatic stem cell identity and stem cells in cancer. I have determined that high Oct1 protein levels correlate with stem cell markers in multiple epithelial tissues, both normal and malignant. Using multiple stem cell matrices, I determined that loss of Oct1 results in a decrease in the stem cell population. Reciprocally, a gain in Oct1 results in an increase in the stem cell population. Also, I found that Oct1 transcriptionally regulates multiple functional stem cell markers, including Aldh1a and Abcg2. Previous studies identified multiple posttranslational modifications to Oct1 protein in HeLa cells, including phosphorylation, glycosylation, and ubiquitination. Here I established that K9 and K403 ubiquitin sites of Oct1 are important for degradation. I determined that Oct1 protein levels are significantly reduced by ~80% in the presence of wildtype BRCA1. However, Oct1 mRNA levels are only reduced less than 2 fold with BRCA1. By mutating the ubiquitin sites from Lysine to Arginine (K9/403R) and transducing stable expression of these mutants, I found that Oct1 protein levels greatly increase in the presence of BRCA1. This indicates that mutating the ubiquitin sites protects Oct1 from BRCA1 dependent degradation, thus supporting my hypothesis that Oct1 is a BRCA1 E3 ubiquitin ligase target.