CD20 homo-oligomers physically associate with the B cell antigen receptor. Dissociation upon receptor engagement and recruitment of phosphoproteins and calmodulin-binding proteins

B cell antigen receptor (BCR) signaling initiates sustained cellular calcium influx necessary for the development, differentiation, and activation of B lymphocytes. CD20 is a B cell-restricted tetraspanning protein organized in the plasma membrane as multimeric molecular complexes involved in BCR-activated calcium entry. Using coprecipitation of native CD20 with tagged or truncated forms of the molecule, we provide here direct evidence of CD20 homo-oligomerization into tetramers. Additionally, the function of CD20 was explored by examining its association with surface-labeled and intracellular proteins before and after BCR signaling. Two major surface-labeled proteins that coprecipitated with CD20 were identified as the heavy and light chains of cell surface IgM, the antigen-binding components of the BCR. After activation, BCR-CD20 complexes dissociated, and phosphoproteins and calmodulin-binding proteins were transiently recruited to CD20. These data provide new evidence of the involvement of CD20 in signaling downstream of the BCR and, together with the previously described involvement of CD20 in calcium influx, the first evidence of physical coupling of the BCR to a calcium entry pathway.     

Critical evaluation of urinary markers for bladder cancer detection and monitoring

Bladder cancer is currently diagnosed using cystoscopy and cytology in patients with suspicious signs and symptoms. These tests are also used to monitor patients with a history of bladder cancer. The recurrence rate for bladder cancer is high, thus necessitating long-term follow-up. Urine cytology has high specificity but low sensitivity for low-grade bladder tumors. Recently, multiple noninvasive urine-based bladder cancer tests have been developed. Although several markers have been approved by the US Food and Drug Administration for bladder cancer surveillance, only a few are approved for detection of bladder cancer in high-risk patients.     

Application of multiplex PCR with histopathologic features for detection of familial breast cancer in formalin-fixed, paraffin-embedded histologic specimens

Breast cancer is the most common malignancy among females in the world. Age and familial history are the major risk factors for the development of this disease in Iran. Mutations of BRCA1 and BRCA2 genes are associated with a greatly increased risk for development of familial breast cancer. Frequency of BRCA mutations was identified in familial breast cancers (FBC) and non-familial breast cancers (NFBC) by molecular genetics, morphological and Immunohistochemical methods. Thirty forth formalin-fixed, paraffin-embedded breast tissue tumors were analyzed from 16 patients with FBC and 18 patients with NFBC. Three 5382insC mutations detected by multiplex PCR in 16 familial breast cancers. Immunohistochemical method was used to detect estrogen receptor (ER) and progesterona receptor (PR) and TP53. Comparison of ER, PR and TP53 exhibited high difference (P < 0.0001) in familial breast cancers and non-familial breast cancers. Our results demonstrated that 5382insC mutation, ER, PR, TP53, mitotic activity, polymorphism, necrosis and tubules can serve as the major risk factors for the development of FBC.     

Drinking water quality and arsenic health risk assessment in Sistan and Baluchestan,Southeastern Province,Iran

Access to drinking water is one of the most important indicators determined by the World Health Organization (WHO). This investigation surveyed the concentration of various pollutants in drinking water and its health risk attribute to Arsenic in Sistan and Baluchistan province, Iran. Water samples were collected from ground water and analyzed for physical parameters, anions, and heavy metals using the standard procedures. The concentrations of sulfate (269 ± 127 mg/l) in five sites exceeded the permissible limit (250 mg/l), while chlorine concentrations (223 ± 100 mg/l) in four sites exceeded the permissible limit (250 mg/l) set by WHO. Similarly, the concentrations of Mg (30 ± 11 mg/l) in four sites exceeded the permissible limit (30 mg/l), while Na concentrations (222 ± 99 mg/l) in five sites exceeded the permissible limit (200 mg/l) set by Institute of Standards and Industrial Research of Iran (ISIRI). In addition, arsenic was in acceptable levels recommended by WHO and local regulations. Based on the calculated indices of hazard qutient (HR) and excess lifetime cancer risk (ELCR), the in-use drinking water has no adverse effects on the consumer's health. Excessive use of fertilizers and pesticides, unsuitable sewerage systems, and inappropriate sludge and solid waste disposal in this province can lead to drinking water pollution. Also, excessive pumping of ground water should be managed as an effective method for supply of safe drinking water.     

Regulation of Mammalian Cone Phototransduction by Recoverin and Rhodopsin Kinase

Cone photoreceptors function under daylight conditions and are essential for color perception and vision with high temporal and spatial resolution. A remarkable feature of cones is that, unlike rods, they remain responsive in bright light. In rods, light triggers a decline in intracellular calcium, which exerts a well studied negative feedback on phototransduction that includes calcium-dependent inhibition of rhodopsin kinase (GRK1) by recoverin. Rods and cones share the same isoforms of recoverin and GRK1, and photoactivation also triggers a calcium decline in cones. However, the molecular mechanisms by which calcium exerts negative feedback on cone phototransduction through recoverin and GRK1 are not well understood. Here, we examined this question using mice expressing various levels of GRK1 or lacking recoverin. We show that although GRK1 is required for the timely inactivation of mouse cone photoresponse, gradually increasing its expression progressively delays the cone response recovery. This surprising result is in contrast with the known effect of increasing GRK1 expression in rods. Notably, the kinetics of cone responses converge and become independent of GRK1 levels for flashes activating more than ∼1% of cone pigment. Thus, mouse cone response recovery in bright light is independent of pigment phosphorylation and likely reflects the spontaneous decay of photoactivated visual pigment. We also find that recoverin potentiates the sensitivity of cones in dim light conditions but does not contribute to their capacity to function in bright light.     

Molecular Systematics of Trilliaceae I. Phylogenetic Analyses of Trillium Using matK Gene Sequences

matK was conducted using 41 Trillium taxa and two out-group taxa (Veratrum maackii and Helonias bullata). A total of 1608 base pairs were analyzed and compared., and then there were 61 variable (36 informative) sites among Trillium species. Fifteen insertion/deletion events (indels) of six or fifteen base pairs were also detected. Phylogenetic analyses of the sequence data revealed that the subgenus Phyllantherum (sessile-flowered species) forms a distinct monophyletic group, whereas the subgenus Trillium (pedicellate-flowered species) does not form a monophyletic group, and is composed of three distinct groups and three basally located species in the tree: (1) the Erectum group, (2) the Grandiflorum group, and (3) the Pusillum group and (4) the three species, including T. govanianum, T. undulatum, and T. rivale. T .rivale appears to be the most basally diverged and a very specialized taxon among the ingroup members. Our matK data indicated that the closest relative of the subgenus Phyllantherum is the Grandiflorum group. The results are concordant with the results of the RFLP analysis of cpDNA and also more or less with those of the cladistic analysis of morphological characters. Received 11 September 1998/ Accepted in revised form 25 December 1998