ABSTRACT
Breast cancer is characterized by oncobiosis, the abnormal composition of the microbiome in neoplastic diseases. The biosynthetic capacity of the oncobiotic flora in breast cancer is suppressed, as suggested by metagenomic studies. The microbiome synthesizes a set of cytostatic and antimetastatic metabolites that are downregulated in breast cancer, including cadaverine, a microbiome metabolite with cytostatic properties. We set out to assess how the protein expression of constitutive lysine decarboxylase (LdcC), a key enzyme for cadaverine production, changes in the feces of human breast cancer patients (n = 35). We found that the fecal expression of Escherichia coli LdcC is downregulated in lobular cases as compared to invasive carcinoma of no special type (NST) cases. Lobular breast carcinoma is characterized by low or absent expression of E-cadherin. Fecal E. coli LdcC protein expression is downregulated in E-cadherin negative breast cancer cases as compared to positive ones. Receiver operating characteristic (ROC) analysis of LdcC expression in lobular and NST cases revealed that fecal E. coli LdcC protein expression might have predictive values. These data suggest that the oncobiotic transformation of the microbiome indeed leads to the downregulation of the production of cytostatic and antimetastatic metabolites. In E-cadherin negative lobular carcinoma that has a higher potential for metastasis formation, the protein levels of enzymes producing antimetastatic metabolites are downregulated. This finding represents a new route that renders lobular cases permissive for metastasis formation. Furthermore, our findings underline the role of oncobiosis in regulating metastasis formation in breast cancer.
ABSTRACT
The precise regulation of the Ca2+ concentration in the endoplasmic reticulum ([Ca2+]er) is important for protein processing and signal transduction. In the pancreatic beta-cell, dysregulation of [Ca2+]er may cause impaired insulin secretion. The Ca2+-sensitive photoprotein aequorin mutated to lower its Ca2+ affinity was stably expressed in the endoplasmic reticulum (ER) of rat insulinoma INS-1 cells. The steady state [Ca2+]er was 267 +/- 9 microM. Both the Ca2+-ATPase inhibitor cyclopiazonic acid and 4-chloro-m-cresol, an activator of ryanodine receptors, caused an almost complete emptying of ER Ca2+. The inositol 1,4,5-trisphosphate generating agonists, carbachol, and ATP, reduced [Ca2+]er by 20-25%. Insulin secretagogues that raise cytosolic [Ca2+] by membrane depolarization increased [Ca2+]er in the potency order K+ >> glucose > leucine, paralleling their actions in the cytosolic compartment. Glucose, which augmented [Ca2+]er by about 25%, potentiated the Ca2+-mobilizing effect of carbachol, explaining the corresponding observation in cytosolic [Ca2+]. The filling of ER Ca2+ by glucose is not directly mediated by ATP production as shown by the continuous monitoring of cytosolic ATP in luciferase expressing cells. Both glucose and K+ increase [Ca2+]er, but only the former generated whereas the latter consumed ATP. Nonetheless, drastic lowering of cellular ATP with a mitochondrial uncoupler resulted in a marked decrease in [Ca2+]er, emphasizing the requirement for mitochondrially derived ATP above a critical threshold concentration. Using alpha-toxin permeabilized cells in the presence of ATP, glucose 6-phosphate did not change [Ca2+]er, invalidating the hypothesis that glucose acts through this metabolite. Therefore, insulin secretagogues that primarily stimulate Ca2+ influx, elevate [Ca2+]er to ensure beta-cell homeostasis.
