Phosphoinositide-specific phospholipase C in normal human liver and in alcohol abuse

Intron retention in PI-PLC γ1 mRNA as a key mechanism affecting MMP expression in human primary fibroblast-like synovial cells

The intron retention (IR) is a phenomenon utilized by cells to allow diverse fates at the same mRNA, leading to a different pattern of synthesis of the same protein. In this study, we analyzed the modulation of phosphoinositide-specific phospholipase C (PI-PLC) enzymes by Harpagophytum procumbens extract (HPE) in synoviocytes from joins of osteoarthritis (OA) patients. In some samples, the PI-PLC γ1 isoform mature mRNA showed the IR and, in these synoviocytes, the HPE treatment increased the phenomenon. Moreover, we highlighted that as a consequence of IR, a lower amount of PI-PLC γ1 was produced. The decrease of PI-PLC γ1 was associated with the decrease of metalloprotease-3 (MMP-3), and MMP-13, and ADAMTS-5 after HPE treatment. The altered expression of MMPs is a hallmark of the onset and progression of OA, thus substances able to decrease their expression are very desirable. The interesting outcomes of this study are that 35% of analyzed synovial tissues showed the IR phenomenon in the PI-PLC γ1 mRNA and that the HPE treatment increased this phenomenon. For the first time, we found that the decrease of PI-PLC γ1 protein in synoviocytes interferes with MMP production, thus affecting the pathways involved in the MMP expression. This finding was validated by the silencing of PI-PLC γ1 in synoviocytes where the IR phenomenon was not present. Our results shed new light on the biochemical mechanisms involved in the degrading enzyme production in the joint of OA patients, suggesting a new therapeutic target and highlighting the importance of personalized medicine.

Synergistic therapeutic effect of combined PDGFR and SGK1 inhibition in metastasis-initiating cells of breast cancer

Lack of insight into the identity of the cells that initiate metastasis hampers the development of antimetastatic therapies. Only a tiny fraction of tumor cells termed metastasis-initiating cells (MICs) are able to successfully seed metastases, causing recurrence and therapeutic resistance. Using metastasis models, we describe a subpopulation of MIC derivates from lung metastases that do not have proliferation advantages, express high levels of the PDGF receptors and EMT/stemness-related genes, and are unique in their ability to initiate metastasis. PDGF factors specifically boost the metastatic potential of MIC populations in a PDGFR-dependent manner. However, PDGFR inhibition preferentially suppresses lung metastases, but does not reduce the primary tumor burden. Thus, we found that PDGFR inhibition blocks AKT activation, whereas SGK1, which shares high-similarity kinase domain and overlap substrates with AKT overexpression remains active in MICs. SGK1 and PDGF signaling act in concert to promote metastatic formation, and SGK1 inhibition confers vulnerability to PDGFR inhibitors, also eliciting a powerful antitumor effect. In vivo, SGK1 inhibitors sensitize xenograft tumors to PDGFR-targeted therapies by reducing primary tumor growth and lung metastasis. Consequently, dual inhibition of PDGFR and SGK1 exhibited strong antitumor activities in established breast cancer cell lines in vitro and in vivo. Therefore, this approach not only provides insight into MIC transformation but also aids the design of improved therapeutic strategies for advanced breast cancer.