Dynamic altruistic cooperation within breast tumors.

BACKGROUND: Social behaviors such as altruism, where one self-sacrifices for collective benefits, critically influence an organism's survival and responses to the environment. Such behaviors are widely exemplified in nature but have been underexplored in cancer cells which are conventionally seen as selfish competitive players. This multidisciplinary study explores altruism and its mechanism in breast cancer cells and its contribution to chemoresistance. METHODS: MicroRNA profiling was performed on circulating tumor cells collected from the blood of treated breast cancer patients. Cancer cell lines ectopically expressing candidate miRNA were used in co-culture experiments and treated with docetaxel. Ecological parameters like relative survival and relative fitness were assessed using flow cytometry. Functional studies and characterization performed in vitro and in vivo include proliferation, iTRAQ-mass spectrometry, RNA sequencing, inhibition by small molecules and antibodies, siRNA knockdown, CRISPR/dCas9 inhibition and fluorescence imaging of promoter reporter-expressing cells. Mathematical modeling based on evolutionary game theory was performed to simulate spatial organization of cancer cells. RESULTS: Opposing cancer processes underlie altruism: an oncogenic process involving secretion of IGFBP2 and CCL28 by the altruists to induce survival benefits in neighboring cells under taxane exposure, and a self-sacrificial tumor suppressive process impeding proliferation of altruists via cell cycle arrest. Both processes are regulated concurrently in the altruists by miR-125b, via differential NF-κB signaling specifically through IKKß. Altruistic cells persist in the tumor despite their self-sacrifice, as they can regenerate epigenetically from non-altruists via a KLF2/PCAF-mediated mechanism. The altruists maintain a sparse spatial organization by inhibiting surrounding cells from adopting the altruistic fate via a lateral inhibition mechanism involving a GAB1-PI3K-AKT-miR-125b signaling circuit. CONCLUSIONS: Our data reveal molecular mechanisms underlying manifestation, persistence and spatial spread of cancer cell altruism. A minor population behave altruistically at a cost to itself producing a collective benefit for the tumor, suggesting tumors to be dynamic social systems governed by the same rules of cooperation in social organisms. Understanding cancer cell altruism may lead to more holistic models of tumor evolution and drug response, as well as therapeutic paradigms that account for social interactions. Cancer cells constitute tractable experimental models for fields beyond oncology, like evolutionary ecology and game theory.

Silencing of the PP2A catalytic subunit causes HER-2/neu positive breast cancer cells to undergo apoptosis.

Protein phosphatase 2A (PP2A), in its activated form as a phosphatase, is a tumour suppressor. However, when PP2A is phosphorylated at the tyrosine residue (pY307), it loses its phosphatase activity and becomes inactivated. In our previous study, we found a higher expression of pY307-PP2A in HER-2/neu positive breast tumour samples and significantly correlated to tumour progression, and in this context, it could function as a proto-oncogene. The above and subsequent findings led us to postulate that the critical role of PP2A in maintaining the balance between cell survival and cell death may be linked to its phosphorylation status at its Y307 residue. Hence, we further investigated the effects of knocking down the PP2A catalytic subunit which contains the Y307 amino acid residue in two HER-2/neu positive breast cancer cell lines, BT474 and SKBR3. We showed that this causes the silenced HER-2/neu breast cancer cells to undergo apoptosis and furthermore, that such apoptosis is mediated by p38 MAPK-caspase 3/PARP activation. Understanding the role of PP2A in HER2/neu positive cells might thus provide insight into new targets for breast cancer therapy.

Tyrosine phosphorylation of PP2A is regulated by HER-2 signalling and correlates with breast cancer progression.

Activation of HER-2/neu leads to multiple signalling cascades and plays a vital role in cell survival and growth. We used a signal transduction antibody array to characterize the tyrosine phosphorylation profiles in heregulin (HRG alpha1)-treated BT474 breast cancer cells, and identified a group of 80 molecules in which tyrosine phosphorylation was highly regulated by HRG-enhanced HER-2/neu signalling. These phosphoproteins included many known HER-2/neu-regulated molecules (e.g., SHC, Akt, Syk and Stat1) and proteins that had not been previously linked to HER-2/neu signalling, such as Fas-associated death domain protein (FADD), apoptosis repressor with CARD domain (ARC), and the tumour suppressor, protein phosphatase type 2A (PP2A). Pharmacological inhibition with HER-2 inhibitor AG825, PI3K inhibitor LY294002, MEK1/2 inhibitor PD98095, and p38MAPK inhibitor SB203580 confirmed that PP2A phosphorylation was modulated by the complicated, HER-2/neu-driven downstream signal network, with the PI3K and MEK1/2 positively, while the p38MAPK negatively regulating its tyrosine phosphorylation. In breast tumour specimens, expression of tyrosine-phosphorylated PP2A (pY307-PP2A) was highly increased in the HER-2/neu positive breast tumours, and significantly correlated to tumour progression, thus enhancing its potential prognostic value. Our data provide meaningful information in the elucidation of the HER-2-driven tyrosine phosphorylation network, and in the development of phosphopeptide-related targets as prognostication indicators.

CD157 undergoes ligand-independent dimerization and colocalizes with caveolin in CHO and MCA102 fibroblasts.

CD157, a glycosylphosphatidylinositol (GPI)-anchored glycoprotein, has recently been shown to induce protein tyrosine phosphorylation in monocytes differentiated from HL-60 cells (mHL-60) in a ligand-dependent manner, but in a ligand-independent manner in stable CD157-transfected CHO (CHO/CD157) and MCA102 (MCA/CD157) fibroblasts [Cell Signal. 11 (1999) 891-897.]. Many GPI-anchored proteins need to be clustered by their ligands or antibodies to induce redistribution to caveolae and a concomitant activation of the associated signal-transducing proteins [Nature 387 (1997) 569-572.]. Here, we demonstrate that CD157, independent of antibody crosslinking, undergoes dimerization with disulfide bond formation and localization in caveolae in CHO/CD157 and MCA/CD157 fibroblasts. However, the native CD157 induced in mHL-60 cells remains a monomer form. The structural integrity of caveolae is required for the association of CD157 with caveolin and CD157-mediated tyrosine kinase signalling in the fibroblasts. We propose that an overexpression of CD157 could lead to its dimerization and relocation to caveolae and to further result in the initiation of signalling processes.

Identification and characterization of nuclear CD38 in the rat spleen.

CD38 is an ectoenzyme, which can produce metabolites with intracellular Ca(2+) mobilizing properties and has multiple immunological functions. However, we have recently shown that CD38 is also localized to the nucleus of rat hepatocyte whereby its metabolite cADPR, is able to mobilize nuclear Ca(2+) stores. In this study, we further characterize the localization of nuclear CD38 in the spleen, an important immune organ. We managed to detect the presence of ADP-ribosyl cyclase activity in the nuclear fraction. With Western blotting, we managed to characterize a 42-45 kDa protein band that is typical of CD38 under reducing and non-reducing conditions. However, as a comparison, other nuclear fractions from tissues like thymus, cardiac muscle and cerebellum yielded an additional 85 kDa protein band under non-reducing conditions. Both protein bands could be blocked with a CD38 blocking peptide. Immunohistochemical studies revealed the expression of CD38 in the marginal zone and in the red pulp. In contrast, the germinal center remained largely immunonegative for CD38. This is the first report of a functionally active ADP-ribosyl cyclase/CD38 in the spleen nuclear fraction. The results here suggest that the presence of CD38 in the nuclear environment might have a corollary to functional and regulatory roles in the nucleus.

Altered CD38 expression in thioacetamide-induced rat model of liver cirrhosis.

BACKGROUND: Cirrhosis is a gradually developing, chronic disease which involves the whole liver. Here, we have shown that CD38 undergoes altered expression upon thioacetamide-induced cirrhosis in rats. CD38 is a type II transmembrane glycoprotein that exhibits ADP-ribosyl cyclase and cADPR hydrolase activities. In this study, the gene and protein expressions of CD38 were investigated in a thioacetamide-induced rat model of cirrhosis. METHODS: CD38 expression was studied by using real-time RT-PCR, immunohistochemistry, and immunoblotting. cADPR content in liver was measured using cycling assay. RESULTS: There was a significant increase in CD38 mRNA and protein expressions as well as ADP-ribosyl cyclase activity in cirrhotic liver compared to the control liver. cADPR level was found to be modestly but significantly augmented in cirrhotic liver. CONCLUSIONS: These results raised the possibility that altered CD38 expression and a concomitant elevation of the enzymatic activity as well as cADPR may be involved in the pathogenesis of liver cirrhosis.

Expression and purification of the recombinant His-tagged GST-CD38 fusion protein using the baculovirus/insect cell expression system.

CD38 is a type II transmembrane glycoprotein found in myriad mammalian tissues and cell types. It is known for its involvement in the metabolism of cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate, two nucleotides with calcium mobilizing activity independent of inositol trisphosphate. CD38 itself has been shown to have clinical significance in certain diseases with possible utilization in diagnostic and prognostic applications. Previous studies on several autoimmune diseases have shown the usefulness of recombinant CD38 protein expressed from Escherichia coli and Pichia pastoris in the detection of autoantibodies to CD38 via Western blot and ELISA. In this study, we produced a 6 x His-tagged GST-CD38 fusion protein using a recombinant baculovirus/insect cell expression technique that was purified as a soluble protein. The fusion protein was purified to homogeneity by affinity and gel filtration chromatography steps. It has an apparent molecular mass of 56 kDa on SDS-PAGE gel stained with Coomassie blue and was recognized on Western blots by antibodies against human CD38 as well as the polyhistidine tag. Peptide mass fingerprinting analysis confirmed the identity of human CD38 in the fusion protein.