Phytoplankton abundance and pigment biomarkers in the oligotrophic, eastern Adriatic estuary.

Phytoplankton distribution and environmental characteristics were determined in a shallow, highly stratified and oligotrophic estuary (Zrmanja, eastern Adriatic). Samples were collected in two contrasting seasons; winter (February 2000), when river discharge was high, and in summer (July 2003), a period of drought. Phytoplankton distribution was closely related to salinity gradients, nutrient levels, and water residence time. Microscopic analysis revealed that phytoplankton was composed mainly of marine diatoms, dinoflagellates, cryptophytes, green flagellates, and coccolithophorids. The dominant biomarker pigments were fucoxanthin, alloxanthin and 19'-hexanoyloxyfucoxanthin, while lower, but indicative contributions of peridinin and chlorophyll b were also noted. Maximum abundance and biomass were found in the middle estuary in winter and in the upper estuary in summer. The estuary is mostly P-limited. Development of chain-forming marine diatoms was evident in winter. Due to the reduced nutrient input in summer, the biomass accumulated in the upper estuary (1,000 ng chlorophyll a l(-1)) was composed mostly of nanoplanktonic unicellular diatoms, nanoplanktonic marine dinoflagellates, cryptophytes, and chlorophytes. The concentrations of about 200 ng l(-1) hex-fuco, suggested that the contribution of prymnesiophytes to total biomass was comparable to that of diatoms and dinoflagellates. In the middle estuary and coastal sea, PO(4) and TIN were 3.5 times lower, resulting in a fivefold decrease in biomass (<100 ng chlorophyll a l(-1)). The oligotrophic Zrmanja and other karstic rivers discharging in the eastern Adriatic Sea, provide insufficient source of nutrients and low productivity of the eastern Adriatic Sea.

Activation of estrogen receptor blocks interleukin-6-inducible cell growth of human multiple myeloma involving molecular cross-talk between estrogen receptor and STAT3 mediated by co-regulator PIAS3.

Estrogen receptors (ERs)(1) highly expressed by multiple myeloma (MM) cells and stimulation of estrogenic ligands leads to cell apoptosis. Interleukin (IL)-6 is a major growth factor in the pathogenesis of MM. However, little is known concerning the molecular consequences of ER activation on IL-6-regulated MM cell growth. Here we show that the ER agonist 17 beta-estradiol completely abolished IL-6-inducible MM cell proliferation. By contrast, the ER antagonist ICI 182,780 overcame the inhibitory effect of estrogen. Estrogen blocked STAT3 DNA binding and transactivation but failed to affect the mRNA expression of IL-6 receptor chains or activation of JAK2 and STAT3. Estrogen-activated ER did not associate directly with STAT3. Estrogen induced the mRNA expression of PIAS3 (protein inhibitor of activated STAT3) and increased PIAS3 physical association with STAT3, suggesting a possible mechanism of STAT3 inhibition requiring PIAS3 as a co-regulator modulating the cross-talk between ER and STAT3. These data directly demonstrate STAT3 to be a molecular participant in ER inhibition of the IL-6 signaling pathway in human MM cells and provides the molecular basis for the potential use of estrogenic ligands in the treatment of MM or other tumors where IL-6 has an autocrine or paracrine role.

Polo-like kinase is a cell cycle-regulated kinase activated during mitosis.

Previously, we demonstrated that expression of polo-like kinase (PLK) is required for cellular DNA synthesis and that overexpression of PLK is sufficient to induce DNA synthesis. We now report that the endogenous levels of PLK, its phosphorylation status, and protein kinase activity are tightly regulated during cell cycle progression. PLK protein is low in G1, accumulates during S and G2M, and is rapidly reduced after mitosis. During mitosis, PLK is phosphorylated on serine, and its serine threonine kinase function is activated at a time close to that of p34cdc2. The phosphorylated form of PLK migrates with reduced mobility on SDS-polyacrylamide gel electrophoresis, and dephosphorylation by purified protein phosphatase 2A converts it to the more rapidly migrating form and reduces the total amount of PLK kinase activity. Purified p34cdc2-cyclin B complex can phosphorylate PLK protein in vitro but causes little increase in PLK kinase activity.