Calreticulin modulates cell adhesiveness via regulation of vinculin expression.

Calreticulin is an ubiquitous and highly conserved high capacity Ca(2+)-binding protein that plays a major role in Ca2+ storage within the lumen of the ER. Here, using L fibroblast cell lines expressing different levels of calreticulin, we show that calreticulin plays a role in the control of cell adhesiveness via regulation of expression of vinculin, a cytoskeletal protein essential for cell-substratum and cell-cell attachments. Both vinculin protein and mRNA levels are increased in cells overexpressing calreticulin and are downregulated in cells expressing reduced level of calreticulin. Abundance of actin, talin, alpha 5 and beta 1 integrins, pp125 focal adhesion kinase, and alpha-catenin is not affected by the differential calreticulin expression. Overexpression of calreticulin increases both cell-substratum and cell-cell adhesiveness of L fibroblasts that, most surprisingly, establish vinculin-rich cell-cell junctions. Upregulation of calreticulin also affects adhesion-dependent phenomena such as cell motility (which decreases) and cell spreading (which increases). Downregulation of calreticulin brings about inverse effects. Cell adhesiveness is Ca2+ regulated. The level of calreticulin expression, however, has no effect on either the resting cytoplasmic Ca2+ concentration or the magnitude of FGF-induced Ca2+ transients. Calreticulin, however, participates in Ca2+ homeostasis as its level of expression affects cell viability at low concentrations of extracellular Ca2+. Consequently, we infer that it is not the Ca2+ storage function of calreticulin that affects cell adhesiveness. Neither endogenous calreticulin nor overexpressed green fluorescent protein-calreticulin construct can be detected outside of the ER. Since all of the adhesion-related effects of differential calreticulin expression can be explained by its regulation of vinculin expression, we conclude that it is the ER-resident calreticulin that affects cellular adhesiveness.

Superficial branch of the radial nerve piercing the brachioradialis tendon to become subcutaneous: an anatomical variation with clinical relevance.

We dissected 20 preserved Caucasian cadaveric upper limbs looking at the relation of the superficial branch of the radial nerve (SBRN) to the brachioradialis tendon. SBRN emerged from deep to superficial position by piercing the brachioradialis tendon near its dorsal border in four limbs. The resulting dorsal tendinous band compressed the nerve and prevented longitudinal gliding movement during ulnar flexion. This is likely to increase the risk of chronic compression neuropathy (Wartenberg's syndrome). In two of these four limbs, there was a communication between the SBRN and lateral cutaneous nerve of the forearm. No such communication was found in the remaining 16 forearms. This communication could contribute to the minimal area of sensory loss observed in Wartenberg's syndrome. We recommend that this anatomical anomaly is looked for and if present dealt with during surgical treatment of Wartenberg's syndrome, as it is likely to predispose to chronic compression neuropathy.

Distal radial and ulnar landmarks used in percutaneous pin fixation: anatomical relationship to the superficial radial and ulnar nerves.

BACKGROUND: The radial and ulnar styloids as well as Lister's tubercle are important surgical landmarks in the surgical treatment of distal forearm fractures. There have been limited studies assessing their relative safety in terms of their distance from superficial nerves which are in danger during surgical procedures. The aim of this cadaveric study was to assess and compare the distance of superficial nerves to these important surgical landmarks. METHODS: Twenty embalmed cadaveric upper limbs were dissected exposing the nerves and tendons around the wrist. The radial styloid, Lister's tubercle, ulnar styloid and nerve branches were marked with pins. The distance of the nearest nerve branch to each landmark was measured with a digital calliper. Statistical analysis of the data was performed using SPSS for Windows 11.5 (SPSS Inc., Chicago, IL) using Friedman Tests and Wilcoxon Signed Ranks tests. RESULTS: The median distance of the nearest nerve branch to the radial styloid was 5.42 mm, to the Lister's tubercle was 16.68 mm and to the ulnar styloid was 13.56 mm. There was unequal safety for these three surgical landmarks regarding proximity to nerve branches (p < 0.00001). Paired comparison using Wilcoxon Signed Ranks Test showed that the Lister's tubercle was safer than the radial styloid (p < 0.0001) and ulnar styloid (p = 0.04). In addition, the ulnar styloid was safer than the radial styloid (p < 0.001). CONCLUSIONS: There is a higher risk of injury to superficial nerves when operating near the radial styloid as it is significantly closer to nerve branches as compared to Lister's tubercle and ulnar styloid.