Role of sphingolipids in oestrogen signalling in breast cancer cells: an update

The signaling pathways activated by the steroid hormone oestrogen include a variety of cytoplasmic second messengers linked to a multitude of tissue-specific effects. In the last decade, sphingolipids and their membrane receptors were added to the list of oestrogen-activated mediators. Oestrogen triggers the sphingolipid signalling cascade in various tissues including breast cancer. Extensive research has shown that sphingolipids are the key regulatory molecules in growth factor networks. Sphingolipids can control the rate of cell proliferation and the differentiation outcome during malignant transformation. In this study, we summarise novel experimental evidences linking sphingolipids to oestrogen-activated effects, highlight the role of sphingolipids in cancer cells and discuss new avenues for future research at the intersection between oestrogen and sphingolipid signalling.

Estrogen defines the dynamics and destination of transactivated EGF receptor in breast cancer cells: role of S1P₃ receptor and Cdc42

Sphingosine-1-phosphate (S1P) receptors mediate transactivation of epidermal growth factor receptor (EGFR) by estrogen (E2). Here we report that the amount of intracellular EGFR remains elevated after stimulation of MCF-7 cells with E2 and S1P, although membrane-localized EGFR and S1P3 receptors are quickly internalized. Co-localization of internalized EGFR and LAMP-2 was lower in cells treated with E2/S1P, suggesting that endosomal EGFR might be directed for recycling instead of degradation. In addition, we found that E2/S1P activated Cdc42 and that knockdown of Cdc42 restores fast EGFR degradation after E2/S1P stimulation. Inhibition of S1P3 receptors prevented E2-induced activation of Cdc42, supporting the important role of the S1P receptor in E2 signaling. This is a novel mechanism further defining the effect of E2/S1P on the EGFR transactivation in breast cancer cells.

An analysis of Q fever patients 6 years after an outbreak in Newport, Wales, UK

BACKGROUND

A cohort of 211 factory workers was exposed to a point source of Q fever in 2002. A total of 38 cases and 14 controls took part in a follow-up study 6 years after the outbreak.

AIM

To compare Q fever serology, the presence of viable Coxiella burnetii, its DNA and fatigue between patients and controls.

DESIGN

Laboratory case study.

METHODS

Q fever serology was by microimmunofluroescence. Viable C. burnetii was detected by VERO cell culture and SCID mice inoculation with patient blood samples. Coxiella burnetii DNA was detected by qPCR (com1 gene) on patients' PBMC and on VERO cultures after 6 weeks incubation. Fatigue was measured by the Chalder Fatigue Scale.

RESULT

At 6 years after the outbreak, 7 of the 38 patients had become seronegative and 4 of the 14 of the controls had become seropositive for Q fever. None of the patient/control peripheral blood mononuclear cells (PBMC) contained viable C. burnetii by VERO cell culture or by SCID mouse inoculation (death or splenomegaly) and none contained C. burnetii DNA by qPCR.

CONCLUSION

Six years after acute Q fever, some patients had become seronegative but none contained viable C. burnetii or its DNA in their PBMC.

Q fever: persistence of antigenic non-viable cell residues of Coxiella burnetii in the host--implications for post Q fever infection fatigue syndrome and other chronic sequelae

BACKGROUND

Our previous studies of persistence of Coxiella burnetii in humans after an initial acute Q fever infection revealed raised, maintained antibody levels and low levels of coxiella genomic DNA at the age of 5 years from onset in Australian patients and at 12 years in patients in the 1989 Birmingham UK Q fever outbreak. Attempts to isolate the coxiella in standard cell culture and susceptible mice by serial passage of PCR positive PBMC and bone marrow were negative.

AIM

To retest PCR positive patient samples by more sensitive methods for viable coxiellas and for the coxiella cell components of antigen and specific lipopolysaccharide (LPS). To re-interpret the previous results in the light of the new information. To review the pertinent literature for a concept of an immuno-modulatory complex generated by the current studies.

DESIGN

Laboratory case study.

METHODS

Stored patient samples were inoculated into SCID mice that were followed for 60 days. Mouse spleen and liver samples were then examined by PCR assay for targets in the COM1 and IS1111a sequences and for antigens by IFA with a polyclonal rabbit antiserum to C. burnetii Phase 1 and a monoclonal antiserum to Phase 1 LPS (details; O. Sukocheva et al., unpublished data).

RESULTS

All specimens, including a recently excised heart valve from a Birmingham patient with late developing endocarditis, were infection negative in SCID mice. Dilutions of SCID mouse spleen and liver homogenates titrated in PCR assays were negative at dilutions attained by control mice inoculated with an endpoint dilution of a viable prototype strain of C. burnetii. Sections of the spleens from all specimens showed a complex of coxiella antigen-LPS by IFA. DISCUSSION/REVIEW: We advance a concept of long-term persistence of a non-infective, non-biodegraded complex of coxiella cell components with its antigens and specific LPS [so called Immunomodulatory complex (IMC)] associated with traces of genomic DNA that signalled its presence in our earlier studies. The IMC's survival in patients for at least 12 years, and in one patient for 70 years implies a capacity for serial passage in macrophages with effective down-regulation of their biodegrading functions. The review assesses the compatibility of the IMC concept in relation to cogent literature on C. burnetii interactions with macrophage and cell-mediated immunity. Some remaining gaps in our knowledge of the organ sites and duration of carriage of viable coxiellas after initial infection are also identified.

Role of sphingolipids in the cytoplasmic signaling of estrogens

Recent studies have clearly demonstrated that estrogen signaling is not limited by the canonical 'genomic' pathway. Estrogens have been shown to interact with multiple cytoplasmic signaling networks including that of growth factors, cytokines, and the most recently recognised participants, sphingolipids. Sphingosine kinase (SphK), a key enzyme in metabolic pathways of sphingolipids, plays an important role in cell signaling and regulates a wide range of biological functions, including the actions of estrogens. Herein we briefly review current experimental evidence showing a critical involvement of sphingolipids in estrogen signaling, especially in breast cancer and vascular endothelial cells. In the current review we mainly focus on the SphK pathway and discuss the potential role of SphK and sphingolipids in the cellular biology of estrogens.