Elucidation of the Complete Biosynthetic Pathway of Phomoxanthone A and Identification of a Para-Para Selective Phenol Coupling Dimerase.

Fungal cytochrome P450 enzymes have been shown to catalyze regio- and stereoselective oxidative intermolecular phenol coupling. However, an enzyme capable of catalyzing undirected para-para (C4-4') coupling has not been reported. Here, we revealed the biosynthetic gene cluster (BGC) of phomoxanthone A from the marine fungus Diaporthe sp. SYSU-MS4722. We heterologously expressed 14 biosynthetic genes in Aspergillus oryzae NSAR1 and found that PhoCDEFGHK is involved in the early stage of phomoxanthone A biosynthesis to give chrysophanol and that chrysophanol is then processed by PhoBJKLMNP to yield penexanthone B. A feeding experiment suggested that PhoO, a cytochrome P450 enzyme, catalyzed the regioselective oxidative para-para coupling of penexanthone B to give phomoxanthone A. The mechanism of PhoO represents a novel enzymatic 4,4'-linkage dimerization method for tetrahydroxanthone formations, which would facilitate biosynthetic engineering of structurally diverse 4,4'-linked dimeric tetrahydroxanthones.

MicroRNA­487b­3p inhibits osteosarcoma chemoresistance and metastasis by targeting ALDH1A3.

Metastasis and chemoresistance indicate poor prognosis in patients with osteosarcoma (OS). In the present study, the expression level of microRNA(miR)­487b­3p in OS specimens and cell lines was found to be decreased, and the expression level of miR­487b­3p was associated with overall survival in patients with OS. The inhibition of miR­487b­3p stimulated OS cell migration and contributed to the development of chemoresistance. In contrast, the overexpression of miR­487b­3p significantly inhibited OS cell migration and enhanced the sensitivity of OS cells to doxorubicin treatment. In addition, the results from the present study revealed that the suppression of miR­487b­3p stimulates OS stemness, while the overexpression of miR­487b­3p suppresses OS stemness. Notably, in vivo experiments also revealed that the overexpression of miR­487b­3p inhibited cancer stem cell (CSC)­induced tumor formation, and the combination treatment of miR­487b­3p and doxorubicin significantly inhibited CSC­induced tumor growth. Furthermore, miR­487b­3p exerts its anticancer role by targeting aldehyde dehydrogenase 1 family member A3 in OS. Taken together, the results from the present study suggests that miR­487b­3p is a tumor suppressor and that the overexpression of miR­487b­3p is a novel strategy to inhibit tumor metastasis and chemoresistance in OS.