Complete solubilization of mammalian cells in lysates.

In conventional cell lysate protocols, cell debris is typically discarded to obtain a cleaner lysate. However, this approach has limitations, as it may overlook vital cellular components. By discarding cell debris, researchers may inadvertently exclude crucial elements. Retaining all cellular components offers several advantages for studying molecular biology within various cellular compartments. Firstly, it provides a more accurate representation of the cellular environment. Secondly, it enables the study of complex cellular interactions, including those involving cellular structures and signaling pathways associated with debris. This shift in perspective highlights the importance of a holistic approach to lysate preparation. By obtaining lysates that include all cellular components, researchers can gain deeper insights into cellular processes, leading to more accurate data and a better understanding of cellular function and dysfunction. This study aimed to develop a protocol for the preparation of total cell lysates that retain all cellular components, including debris. Our method involves:•A three-step solubilization process using a combination of detergents, saccharides, and chelators, coupled with sonication, in contrast to the classical one-step approach using an all-detergent cocktail.•A comprehensive strategy ensuring the solubilization of all cellular components, providing a more complete lysate for analysis.

Intracellular cartilage oligomeric matrix protein augments breast cancer resistance to chemotherapy.

Chemotherapy persists as the primary intervention for breast cancer, with chemoresistance posing the principal obstacle to successful treatment. Herein, we show that cartilage oligomeric matrix protein (COMP) expression leads to increased cancer cell survival and attenuated apoptosis under treatment with several chemotherapeutic drugs, anti-HER2 targeted treatment, and endocrine therapy in several breast cancer cell lines tested. The COMP-induced chemoresistance was independent of the breast cancer subtype. Extracellularly delivered recombinant COMP failed to rescue cells from apoptosis while endoplasmic reticulum (ER)-restricted COMP-KDEL conferred resistance to apoptosis, consistent with the localization of COMP in the ER, where it interacted with calpain. Calpain activation was reduced in COMP-expressing cells and maintained at a lower level of activation during treatment with epirubicin. Moreover, the downstream caspases of calpain, caspases -9, -7, and -3, exhibited significantly reduced activation in COMP-expressing cells under chemotherapy treatment. Chemotherapy, when combined with calpain activators, rendered the cells expressing COMP more chemosensitive. Also, the anti-apoptotic proteins phospho-Bcl2 and survivin were increased in COMP-expressing cells upon chemotherapy. Cells expressing a mutant COMP lacking thrombospondin repeats exhibited reduced chemoresistance compared to cells expressing full-length COMP. Evaluation of calcium levels in the ER, cytosol, and mitochondria revealed that COMP expression modulates intracellular calcium homeostasis. Furthermore, patients undergoing chemotherapy or endocrine therapy demonstrated significantly reduced overall survival time when tumors expressed high levels of COMP. This study identifies a novel role of COMP in chemoresistance and calpain inactivation in breast cancer, a discovery with potential implications for anti-cancer therapy.