Structural and biophysical properties of the integrin-associated cytoskeletal protein talin

Talin is a large cytoskeletal protein (2541 amino acid residues) which plays a key role in integrin-mediated events that are crucial for cell adhesion, migration, proliferation and survival. This review summarises recent work on the structure of talin and on some of the structurally better defined interactions with other proteins. The N-terminal talin head (approx. 50 kDa) consists of an atypical FERM domain linked to a long flexible rod (approx. 220 kDa) made up of a series of amphipathic helical bundle domains. The F3 FERM subdomain in the head binds the cytoplasmic tail of integrins, but this interaction can be inhibited by an interaction of F3 with a helical bundle in the talin rod, the so-called “autoinhibited form” of the molecule. The talin rod contains a second integrin-binding site, at least two actin-binding sites and a large number of binding sites for vinculin, which is important in reinforcing the initial integrin–actin link mediated by talin. The vinculin binding sites are defined by hydrophobic residues buried within helical bundles, and these must unfold to allow vinculin binding. Recent experiments suggest that this unfolding may be mediated by mechanical force exerted on the talin molecule by actomyosin contraction

Kindlins, Integrin Activation and the Regulation of Talin Recruitment to αIIbβ3

Talins and kindlins bind to the integrin β3 cytoplasmic tail and both are required for effective activation of integrin αIIbβ3 and resulting high-affinity ligand binding in platelets. However, binding of the talin head domain alone to β3 is sufficient to activate purified integrin αIIbβ3 in vitro. Since talin is localized to the cytoplasm of unstimulated platelets, its re-localization to the plasma membrane and to the integrin is required for activation. Here we explored the mechanism whereby kindlins function as integrin co-activators. To test whether kindlins regulate talin recruitment to plasma membranes and to αIIbβ3, full-length talin and kindlin recruitment to β3 was studied using a reconstructed CHO cell model system that recapitulates agonist-induced αIIbβ3 activation. Over-expression of kindlin-2, the endogenous kindlin isoform in CHO cells, promoted PAR1-mediated and talin-dependent ligand binding. In contrast, shRNA knockdown of kindlin-2 inhibited ligand binding. However, depletion of kindlin-2 by shRNA did not affect talin recruitment to the plasma membrane, as assessed by sub-cellular fractionation, and neither over-expression of kindlins nor depletion of kindlin-2 affected talin interaction with αIIbβ3 in living cells, as monitored by bimolecular fluorescence complementation. Furthermore, talin failed to promote kindlin-2 association with αIIbβ3 in CHO cells. In addition, purified talin and kindlin-3, the kindlin isoform expressed in platelets, failed to promote each other's binding to the β3 cytoplasmic tail in vitro. Thus, kindlins do not promote initial talin recruitment to αIIbβ3, suggesting that they co-activate integrin through a mechanism independent of recruitment

Early Access Program Results From Turkey and a Literature Review on Daratumumab Monotherapy Among Heavily Pretreated Patients With Relapsed/Refractory Myeloma.

BACKGROUND: In countries where frontline drug approval is limited to first-generation proteasome inhibitors or immunomodulatory drugs, relapses have been both more frequent and less durable. We investigated real world data on the efficacy and safety of daratumumab monotherapy among patients with relapsed refractory multiple myeloma (RRMM) from Turkey using a prospective early access program. PATIENTS AND METHODS: A total of 42 patients with RRMM after a minimum of 3 previous lines of proteasome inhibitor/immunomodulatory drug-based treatments were included from 25 centers across Turkey. Daratumumab monotherapy was administered intravenously at a dose of 16 mg/kg weekly (cycles 1-2), on alternate weeks (cycles 3-6), and monthly thereafter. RESULTS: The median daratumumab monotherapy duration was 5.5 months (range, 0.2-28.7 months). The overall response rate was 45.2%, including 14 (33.3%) partial responses, 4 (9.5%) very good partial responses, and 1 (2.4%) complete response. The median duration of response was 4.9 months. The median progression-free survival (PFS) was 5.5 (95% confidence interval, 2.6-8.4 months) with 12- and 18-month PFS rates of 35.7% and 31.0%, respectively. The median overall survival was not reached; the 12- and 18-month overall survival rates were 64.3% and 59.5%, respectively. The depth of response had a significant effect on PFS (log-rank test, P = .026). Overall, of the 76 adverse events reported, 33 (43.4%) were grade ≥ 3; only 4 (9.52%) were grade 3 infusion-related reactions. No infusion-related reactions or adverse events led to treatment discontinuation. CONCLUSION: The present findings from our daratumumab early access program have confirmed the efficacy and safety profile of daratumumab monotherapy in heavily pretreated Turkish patients with RRMM