The microvillar protocadherin CDHR5 associates with EBP50 to promote brush border assembly

Transporting epithelial cells of the gut and kidney interact with their luminal environment through a densely packed collection of apical microvilli known as a brush border (BB). Proper brush border assembly depends on the intermicrovillar adhesion complex (IMAC), a protocadherin-based adhesion complex found at the distal tips of microvilli that mediates adhesion between neighboring protrusions to promote their organized packing. Loss of the IMAC adhesion molecule Cadherin-related family member 5 (CDHR5) results in significant brush border defects, though the functional properties of this protocadherin have not been thoroughly explored. Here, we show that the cytoplasmic tail of CDHR5 contributes to its correct apical targeting and functional properties in an isoform-specific manner. Library screening identified the Ezrin-associated scaffolds EBP50 and E3KARP as cytoplasmic binding partners for CDHR5. Consistent with this, loss of EBP50 disrupted proper brush border assembly with cells exhibiting markedly reduced apical IMAC levels. Together, our results shed light on the apical targeting determinants of CDHR5 and further define the interactome of the IMAC involved in brush border assembly.

Comparative analysis of the MyTH4-FERM myosins reveals insights into the determinants of actin track selection in polarized epithelia

MyTH4-FERM (MF) myosins evolved to play a role in the creation and function of a variety of actin-based membrane protrusions that extend from cells. Here we performed an analysis of the MF myosins, Myo7A, Myo7B, and Myo10, to gain insight into how they select for their preferred actin networks. Using enterocytes that create spatially separated actin tracks in the form of apical microvilli and basal filopodia, we show that actin track selection is principally guided by the mode of oligomerization of the myosin along with the identity of the motor domain, with little influence from the specific composition of the lever arm. Chimeric variants of Myo7A and Myo7B fused to a leucine zipper parallel dimerization sequence in place of their native tails both selected apical microvilli as their tracks, while a truncated Myo10 used its native antiparallel coiled-coil to traffic to the tips of filopodia. Swapping lever arms between the Class 7 and 10 myosins did not change actin track preference. Surprisingly, fusing the motor-neck region of Myo10 to a leucine zipper or oligomerization sequences derived from the Myo7A and Myo7B cargo proteins USH1G and ANKS4B, respectively, re-encoded the actin track usage of Myo10 to apical microvilli with significant efficiency.

A cryptic sequence targets the adhesion complex scaffold ANKS4B to apical microvilli to promote enterocyte brush border assembly

Nutrient-transporting enterocytes interact with their luminal environment using a densely packed collection of apical microvilli known as the brush border. Assembly of the brush border is controlled by the intermicrovillar adhesion complex (IMAC), a protocadherin-based complex found at the tips of brush border microvilli that mediates adhesion between neighboring protrusions. ANKS4B is known to be an essential scaffold within the IMAC, although its functional properties have not been thoroughly characterized. We report here that ANKS4B is directed to the brush border using a noncanonical apical targeting sequence that maps to a previously unannotated region of the scaffold. When expressed on its own, this sequence targeted to microvilli in the absence of any direct interaction with the other IMAC components. Sequence analysis revealed a coiled-coil motif and a putative membrane-binding basic-hydrophobic repeat sequence within this targeting region, both of which were required for the scaffold to target and mediate brush border assembly. Size-exclusion chromatography of the isolated targeting sequence coupled with in vitro brush border binding assays suggests that it functions as an oligomer. We further show that the corresponding sequence found in the closest homolog of ANKS4B, the scaffold USH1G that operates in sensory epithelia as part of the Usher complex, lacks the inherent ability to target to microvilli. This study further defines the underlying mechanism of how ANKS4B targets to the apical domain of enterocytes to drive brush border assembly and identifies a point of functional divergence between the ankyrin repeat-based scaffolds found in the IMAC and Usher complex.

The small EF-hand protein CALML4 functions as a critical myosin light chain within the intermicrovillar adhesion complex

Specialized transporting and sensory epithelial cells employ homologous protocadherin-based adhesion complexes to remodel their apical membrane protrusions into organized functional arrays. Within the intestine, the nutrient-transporting enterocytes utilize the intermicrovillar adhesion complex (IMAC) to assemble their apical microvilli into an ordered brush border. The IMAC bears remarkable homology to the Usher complex, whose disruption results in the sensory disorder type 1 Usher syndrome (USH1). However, the entire complement of proteins that comprise both the IMAC and Usher complex are not yet fully elucidated. Using a protein isolation strategy to recover the IMAC, we have identified the small EF-hand protein calmodulin-like protein 4 (CALML4) as an IMAC component. Consistent with this finding, we show that CALML4 exhibits marked enrichment at the distal tips of enterocyte microvilli, the site of IMAC function, and is a direct binding partner of the IMAC component myosin-7b. Moreover, distal tip enrichment of CALML4 is strictly dependent upon its association with myosin-7b, with CALML4 acting as a light chain for this myosin. We further show that genetic disruption of CALML4 within enterocytes results in brush border assembly defects that mirror the loss of other IMAC components and that CALML4 can also associate with the Usher complex component myosin-7a. Our study further defines the molecular composition and protein-protein interaction network of the IMAC and Usher complex and may also shed light on the etiology of the sensory disorder USH1H.

Increased Risk of CHD in the Presence of rs7865618 (A allele): Tehran Lipid and Glucose Study

BACKGROUND

Recent genome-wide association studies (GWAS) in European populations have indicated that the rs12526453 polymorphism located in phosphatase and actin regulator 1 gene (PHACTR1), mapping to chromosome 6p24 and rs7865618 polymorphism in the cyclin-dependent kinase inhibitor B antisense RNA 1 gene (CDKN2B-AS1) on 9p21.3 are associated with coronary heart disease (CHD). This study was carried out to investigate the association of these polymorphisms and CHD in an Iranian population.

METHODS

In the present case-control study, 420 patients with CHD events were recruited from the population of the Tehran lipid and glucose study (TLGS); 407 healthy controls matched for age and sex were selected from the same population. The SNPs rs12526453 and rs7865618 were genotyped using amplification refractory mutation system-polymerase chain reaction (ARMS-PCR).

RESULTS

The allele frequency of both SNPs deviated from Hardy-Weinberg equilibrium. The C allele frequency of the rs12526453 (68.5%, P = 0.11) and A allele of the rs7865618 (68.8%, P = 0.09) were the most prevalent alleles in both the case and control groups. The results indicated a significant association between the presence of risk alleles of rs7865618 and CHD in the TLGS population (P = 0.03; OR: 1.73; CI95%: 1.04 - 2.88).

CONCLUSION

Due to the importance of chromosome 9p21 region and its relation with cardiovascular disease, the allelic pattern of its variation should be studied in different populations. The relation between this polymorphism and cardiovascular disease in the studied population confirms the importance of this region.

Effectiveness of mindfulness training and dietary regime on weight loss in obese people

The present research was aimed to investigate the effectiveness of mindfulness training and dietary regime on weight loss in obese people. The research was quasi-experimental with posttest-pretest that used control group. The population consisted of all the individuals who attended two clinics of nutrition advice and diet therapy in Karaj. 60 individuals, whose BMI was more than 30, were selected by using the random sampling method. Moreover, they were evaluated by using the SCL-90 test in order to neglect them in case there existed any other significant disorder. Next, they were selected based on age, sex, and education. After explaining the individuals the ongoing research and collecting the informed consent written by them, the samples were placed in four groups (15 in each group). The groups that received mindfulness training attended the nutrition center for eight to 120-minute sessions. In addition, since all the participants referred to the center were motivated to lose weight, individuals who were placed in the control group and those who received mindfulness training were asked not to follow any specific diet for two months. Moreover, the in depth relaxation CD was prepared for those who asked, in order to train themselves at home. Descriptive statistical methods were employed in order to analyze the data and ANACOVA and variance analysis with frequent measurement were used. The research findings indicated that mindfulness training was accompanied by diet, which resulted in weight loss in obese patients. In addition, the findings of the two-month follow-up indicated lasting results.