HOXB8 expression in ovarian serous carcinoma effusions is associated with shorter survival.

OBJECTIVE: HOX proteins are key transcription factors in embryogenesis. HOXB5 and HOXB8 were previously shown to be overexpressed in ovarian/primary peritoneal serous carcinoma compared to breast carcinoma using gene expression arrays. The present study investigated the clinical role of HOXB5 and HOXB8 in advanced-stage (FIGO III-IV) ovarian serous carcinoma. METHODS: HOXB5 and HOXB8 protein expression was analyzed in 286 effusions and 76 patient-matched solid lesions (27 primary carcinomas, 49 metastases) using immunohistochemistry. Expression was analyzed for association with clinicopathologic parameters, including survival. RESULTS: Cytoplasmic HOXB5 protein was detected in 268/286 (94%) effusions. HOXB8 was expressed at both the cytoplasm (252/286; 88%) and nucleus (131/286; 46%) of carcinoma cells. Cytoplasmic HOXB5, cytoplasmic HOXB8 and nuclear HOXB8 were found in 56/76 (74%), 76/76 (100%) and 30/76 (39%) solid lesions, respectively, with significantly higher HOXB5 expression in effusions (p=0.002) and higher cytoplasmic HOXB8 in solid lesions (p<0.001). HOXB5 expression was higher in post-chemotherapy disease recurrence effusions compared to pre-chemotherapy effusions tapped at diagnosis (p=0.04). In univariate survival analysis of the effusion cohort, higher expression of cytoplasmic HOXB8 was associated with significantly shorter progression-free survival (p=0.033), whereas higher nuclear HOXB8 expression was associated with significantly shorter overall survival in analysis limited to patients with post-chemotherapy effusions (p=0.036). Neither finding was independent prognostic factor in Cox multivariate analysis. CONCLUSIONS: HOXB5 and HOXB8 are frequently expressed in ovarian serous carcinoma, with anatomic site-related differences for cytoplasmic staining. HOXB5 may be affected by chemotherapy in effusions. HOXB8 expression is associated with shorter survival in metastatic serous carcinoma.

Lettuce costunolide synthase (CYP71BL2) and its homolog (CYP71BL1) from sunflower catalyze distinct regio- and stereoselective hydroxylations in sesquiterpene lactone metabolism.

Sesquiterpene lactones (STLs) are terpenoid natural products possessing the γ-lactone, well known for their diverse biological and medicinal activities. The occurrence of STLs is sporadic in nature, but most STLs have been isolated from plants in the Asteraceae family. Despite the implication of the γ-lactone group in many reported bioactivities of STLs, the biosynthetic origins of the γ-lactone ring remains elusive. Germacrene A acid (GAA) has been suggested as a central precursor of diverse STLs. The regioselective (C6 or C8) and stereoselective (α or ß) hydroxylation on a carbon of GAA adjacent to its carboxylic acid at C12 is responsible for the γ-lactone formation. Here, we report two cytochrome P450 monooxygenases (P450s) capable of catalyzing 6α- and 8ß-hydroxylation of GAA from lettuce and sunflower, respectively. To identify these P450s, sunflower trichomes were isolated to generate a trichome-specific transcript library, from which 10 P450 clones were retrieved. Expression of these clones in a yeast strain metabolically engineered to synthesize substrate GAA identified a P450 catalyzing 8ß-hydroxylation of GAA, but the STL was not formed by spontaneous lactonization. Subsequently, we identified the closest homolog of the GAA 8ß-hydroxylase from lettuce and discovered 6α-hydroxylation of GAA by the recombinant enzyme. The resulting 6α-hydroxy-GAA spontaneously undergoes a lactonization to yield the simplest form of STL, costunolide. Furthermore, we demonstrate the milligram per liter scale de novo synthesis of costunolide using the lettuce P450 in an engineered yeast strain, an important advance that will enable exploitation of STLs. Evolution and homology models of these two P450s are discussed.

Biochemical conservation and evolution of germacrene A oxidase in asteraceae.

Sesquiterpene lactones are characteristic natural products in Asteraceae, which constitutes approximately 8% of all plant species. Despite their physiological and pharmaceutical importance, the biochemistry and evolution of sesquiterpene lactones remain unexplored. Here we show that germacrene A oxidase (GAO), evolutionarily conserved in all major subfamilies of Asteraceae, catalyzes three consecutive oxidations of germacrene A to yield germacrene A acid. Furthermore, it is also capable of oxidizing non-natural substrate amorphadiene. Co-expression of lettuce GAO with germacrene synthase in engineered yeast synthesized aberrant products, costic acids and ilicic acid, in an acidic condition. However, cultivation in a neutral condition allowed the de novo synthesis of a single novel compound that was identified as germacrene A acid by gas and liquid chromatography and NMR analyses. To trace the evolutionary lineage of GAO in Asteraceae, homologous genes were further isolated from the representative species of three major subfamilies of Asteraceae (sunflower, chicory, and costus from Asteroideae, Cichorioideae, and Carduoideae, respectively) and also from the phylogenetically basal species, Barnadesia spinosa, from Barnadesioideae. The recombinant GAOs from these genes clearly showed germacrene A oxidase activities, suggesting that GAO activity is widely conserved in Asteraceae including the basal lineage. All GAOs could catalyze the three-step oxidation of non-natural substrate amorphadiene to artemisinic acid, whereas amorphadiene oxidase diverged from GAO displayed negligible activity for germacrene A oxidation. The observed amorphadiene oxidase activity in GAOs suggests that the catalytic plasticity is embedded in ancestral GAO enzymes that may contribute to the chemical and catalytic diversity in nature.