IntroductionRhoB has been reported to exert positive and negative effects on cancer pathophysiology but an understanding of its role in breast cancer remains incomplete. Analysis of data from the Oncomine database showed a positive correlation between RhoB expression and positivity for both estrogen receptor alpha (ERα) and progesterone receptor (PR).MethodsThis finding was validated by our analysis of a tissue microarray constructed from a cohort of 113 patients and then investigated in human cell models.ResultsWe found that RhoB expression in tissue was strongly correlated with ERα and PR expression and inversely correlated with tumor grade, tumor size and count of mitosis. In human breast cancer cell lines, RhoB attenuation was associated with reduced expression of both ERα and PR, whereas elevation of RhoB was found to be associated with ERα overexpression. Mechanistic investigations suggested that RhoB modulates ERα expression, controlling both its protein and mRNA levels, and that RhoB modulates PR expression by accentuating the recruitment of ERα and other major co-regulators to the promoter of PR gene. A major consequence of RhoB modulation was that RhoB differentially regulated the proliferation of breast cancer cell lines. Interestingly, we documented crosstalk between RhoB and ERα, with estrogen treatment leading to RhoB activation.ConclusionTaken together, our findings offer evidence that in human breast cancer RhoB acts as a positive function to promote expression of ERα and PR in a manner correlated with cell proliferation.

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Dear Sir,The ability of the lipidic mediator prostaglandin E 2 (PGE 2 ) to regulate the immune system has been widely explored in the past decade.1,2 Numerous studies have highlighted the ability of PGE 2 to regulate monocyte macrophages, dendritic cells, as well as T and B lymphocytes.1,2 The biologic effects of PGE 2 are mediated through interactions with 4 distinct membrane-bound G-protein-coupled EP receptors: EP 1 , EP 2 , EP 3 and EP 4 . EP 1 is coupled to G q/p and ligand binding induces intracellular calcium levels. EP 3 is coupled to G i and inhibits cAMP production. In contrast, EP 2 and EP 4 are coupled to G s and stimulate cAMP production, which leads to gene regulation.1 Freshly isolated blast cells of acute myeloid leukemic (AML) and acute lymphoid leukemic (ALL) patients increase their cAMP synthesis in response to forskolin, a cAMP-induced agonist.3 While the presence of functional EP receptors on mature leukocytes is documented, 4 no results are available concerning their presence on immature ones. In view of the potentially important role of PGE 2 in processes of cancer and leukocyte maturation and function, 1,2 we investigated the presence of EP 2 and EP 4 receptors on freshly isolated blast cells from AML and ALL patients by testing the effect of PGE 2 on their cAMP synthesis.Over a period of 1 year, blood samples recovered on EDTA were obtained from 12 consecutive patients (6 men, 6 women; mean age, 66 years) at diagnosis according to the Helsinki recommendations. Blood samples from patients with more than 85% (range, 85-97%) blast cells as circulating leukocytes were used. Leucocytosis ranged from 11 to 210 G/l. The population (graded according to the French-American-British classification) consisted of 2 AML0, 3 AML1, 2 AML2, 1 AML3, 1 AML4, 1 AML5 and 2 ALL2. Cytogenetic data were available for 11 patients. Six had a normal karyotype. The 5 remaining patients were heterogeneous and comprised one complex karyotype, one with a Philadelphia chromosome, one with a t(15;17), one with an unidentified marker and one with a monosomy 7. Blood mononuclear cells were isolated by separation on a Ficoll gradient and washed 2 times with Hank's balanced salts solution (HBSS). The blast purity (mean, 98%; range, 94-99%) was controlled by flow cytometry analysis (XL II; Coulter, Margency, France). Blast viability (> 95%) was judged by Trypan blue exclusion. Blasts (3 Â 10 6 cells) were stimulated in HBSS with PGE 2 and various EP-specific agonists for 10 min at 378C. In separate sets of experiments, the effect of PGE 2 on cAMP production was investigated in a cell-and timedependent manner. After stimulation, cells were ethanol-extracted and cAMP levels were measured using a commercially available EIA kit (Cayman Chemical, Ann Arbor, MI) according to the manufacturer's instructions. The sensitivity of the assay permits detection of 0.1 pmol cAMP. In another set of experiments, EP 2 receptors were studied by reverse transcription-polymerase chain reaction (RT-PCR).Results indicate that PGE 2 stimulated cAMP...