UXT Is a LOX-PP Interacting Protein That Modulates Estrogen Receptor Alpha Activity in Breast Cancer Cells.

The lysyl oxidase proenzyme propeptide region (LOX-PP) is a tumor suppressor protein whose mechanism of action is not completely understood. Here, the Ubiquitously expressed Transcript (UXT) was identified in a yeast two-hybrid assay with LOX-PP as bait and confirmed as a novel LOX-PP associating protein. UXT, a prefoldin-like protein, is ubiquitous in human and mouse. Since UXT modulates androgen receptor transcriptional activity in prostate cancer, we studied its role in breast cancer. Breast tumors and derived cell lines overexpressed UXT. UXT was able to associate with the estrogen receptor alpha (ER) and decrease its transcriptional activity and target gene expression. Conversely, UXT knockdown increased ER element-dependent transcriptional activity. Ectopic LOX-PP relocalized UXT to the cytoplasm and decreased its stability. UXT ubiquitination and depletion in the presence of LOX-PP was rescued by a proteasomal inhibitor. In summary, proteasome-mediated turnover of UXT upon interaction with LOX-PP releases repression of ER transcriptional activity. J. Cell. Biochem. 118: 2347-2356, 2017. © 2017 Wiley Periodicals, Inc.

The lysyl oxidase propeptide interacts with the receptor-type protein tyrosine phosphatase kappa and inhibits ß-catenin transcriptional activity in lung cancer cells.

The propeptide region of the lysyl oxidase proenzyme (LOX-PP) has been shown to inhibit Ras signaling in NIH 3T3 and lung cancer cells with activated RAS, but its mechanism of action is poorly understood. Here, a yeast two-hybrid assay of LOX-PP-interacting proteins identified a clone encoding the intracellular phosphatase domains of receptor-type protein tyrosine phosphatase kappa (RPTP-κ), and the interaction of the two proteins in mammalian cells was confirmed. RPTP-κ is proteolytically processed to isoforms that have opposing effects on ß-catenin activity. The RPTP-κ transmembrane P subunit interacts with and sequesters ß-catenin at the cell membrane, where it can associate with E-cadherin and promote intercellular interactions. At high cell density, further processing of the P subunit yields a phosphatase intracellular portion (PIC) subunit, which chaperones ß-catenin to the nucleus, where it can function to activate transcription. Lung cancer cells were found to contain higher PIC levels than untransformed lung epithelial cells. In H1299 lung cancer cells, ectopic LOX-PP expression reduced the nuclear levels of PIC by increasing its turnover in the lysosome, thereby decreasing the nuclear levels and transcriptional activity of ß-catenin while increasing ß-catenin membrane localization. Thus, LOX-PP is shown to negatively regulate pro-oncogenic ß-catenin signaling in lung cancer cells.

RelB NF-kappaB represses estrogen receptor alpha expression via induction of the zinc finger protein Blimp1.

Aberrant constitutive expression of NF-kappaB subunits, reported in more than 90% of breast cancers and multiple other malignancies, plays pivotal roles in tumorigenesis. Higher RelB subunit expression was demonstrated in estrogen receptor alpha (ERalpha)-negative breast cancers versus ERalpha-positive ones, due in part to repression of RelB synthesis by ERalpha signaling. Notably, RelB promoted a more invasive phenotype in ERalpha-negative cancers via induction of the BCL2 gene. We report here that RelB reciprocally inhibits ERalpha synthesis in breast cancer cells, which contributes to a more migratory phenotype. Specifically, RelB is shown for the first time to induce expression of the zinc finger repressor protein Blimp1 (B-lymphocyte-induced maturation protein), the critical mediator of B- and T-cell development, which is transcribed from the PRDM1 gene. Blimp1 protein repressed ERalpha (ESR1) gene transcription. Commensurately higher Blimp1/PRDM1 expression was detected in ERalpha-negative breast cancer cells and primary breast tumors. Induction of PRDM1 gene expression was mediated by interaction of Bcl-2, localized in the mitochondria, with Ras. Thus, the induction of Blimp1 represents a novel mechanism whereby the RelB NF-kappaB subunit mediates repression, specifically of ERalpha, thereby promoting a more migratory phenotype.