Mixing and matching methylotrophic enzymes to design a novel methanol utilization pathway in E. coli

One-carbon (C1) compounds, such as methanol, have recently gained attention as alternative low-cost and non-food feedstocks for microbial bioprocesses. Considerable research efforts are thus currently focused on the generation of synthetic methylotrophs by transferring methanol assimilation pathways into established bacterial production hosts. In this study, we used an iterative combination of dry and wet approaches to design, implement and optimize this metabolic trait in the most common chassis, E. coli. Through in silico modelling, we designed a new route that "mixed and matched" two methylotrophic enzymes: a bacterial methanol dehydrogenase (Mdh) and a dihydroxyacetone synthase (Das) from yeast. To identify the best combination of enzymes to introduce into E. coli, we built a library of 266 pathway variants containing different combinations of Mdh and Das homologues and screened it using high-throughput ¹³C-labeling experiments. The highest level of incorporation of methanol into central metabolism intermediates (e.g. 22% into the PEP), was obtained using a variant composed of a Mdh from A. gerneri and a codon-optimized version of P. angusta Das. Finally, the activity of this new synthetic pathway was further improved by engineering strategic metabolic targets identified using omics and modelling approaches. The final synthetic strain had 1.5 to 5.9 times higher methanol assimilation in intracellular metabolites and proteinogenic amino acids than the starting strain did. Broadening the repertoire of methanol assimilation pathways is one step further toward synthetic methylotrophy in E. coli.

Expression and regulation of the estrogen receptors in PC-3 human prostate cancer cells

The aim of this study was to identify the expression, cellular localization and regulation of classic estrogen receptors ERα and ERβ, ER-α36 isoform and GPER in the androgen-independent prostate cancer cell line PC-3. In addition, we evaluated the relative contribution of these receptors to the activation of the ERK1/2 (extracellular signal-regulated protein kinases) signaling pathway. These four estrogen receptors were detected by Western blot assays and were shown by immunofluorescence assays to localize preferentially in extranuclear regions of PC-3 cells. In addition, treatment with 17β-estradiol (E2) (1 μM) for 24 h led to down-regulation of the classic estrogen receptors, whereas E2 at physiological concentration (0.1 nM) for 24h tended to increase the levels of ERα and ERβ. Furthermore, the ERα-selective agonist PPT selectively increased the expression of ERβ and the ERβ-selective agonist DPN increased ERα levels. None of these treatments affected expression of the ER-α36 isoform. The unusual cytoplasmic localization of the classic estrogen receptors in these cells differs from the nuclear localization in the majority of estrogen target cells and suggests that rapid signaling pathways may be preferentially activated. In fact, treatment with selective agonists of ERα, ERβ and GPER induced ERK1/2 phosphorylation that was blocked by the respective antagonists. On the other hand, activation of ERK1/2 induced by E2 may involve additional mechanisms because it was not blocked by the three antagonists. Taken together, the results indicate that there is a crosstalk between ERα and ERβ to regulate the expression of each other, and suggest the involvement of other receptors, such as ER-α36, in the rapid ERK1/2 activation by E2. The identification of new isoforms of ERs, regulation of the receptors and signaling pathways is important to develop new therapeutic strategies for the castration-resistant prostate cancer.