PDIA3 is a member of the protein disulfide isomerase family mainly found in the endoplasmic reticulum. Here, it modulates the folding of newly synthesized glycoproteins by means of its redox and chaperon activity promoting proper disulfide bond formation [1]. PDIA3 is ubiquitously expressed in all tissues although with different concentrations for each of them and it has distinct sub-cellular localizations. PDIA3 dysregulation is involved in several human pathologies including neurodegenerative and metabolic diseases, as well as in different types of cancer, in platelet aggregation and musculoskeletal disorders [2]. Considering PDIA3 flexible binding sites able to interact with a series of small ligands, e.g. flavonoids, I would characterize thermodynamic parameters, binding constants and effects on enzymatic activity of the interaction between PDIA3 and a flavonoids range [3]. So far, two flavonoids, silibinin and punicalagin, showed the ability to bind and modify PDIA3 properties in the micromolar range of concentration [4,5]. To verify if silibinin and punicalagin binding effects are only PDIA3specific, it will be performed a comparative study between PDIA1 and PDIA3. Flavonoids binding and the effects on both proteins will be evaluated by quenching analysis of the protein intrinsic fluorescence, differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC) assays, whereas the disulfide-reductase activity will be assayed using dieosin glutathione disulfide. From preliminary studies the two flavonoids exhibit different behaviours on both PDIAs suggesting that the PDIA/flavonoid interactions involve different binding sites. Dynamic studies could elucidate the complex PDIA/flavonoid interplay. Silibinin and punicalagin ability to modulate PDIAs could be used in the treatment of diseases in which PDIAs are overexpressed or play important roles, and as adjuvant in chemotherapy promoting endoplasmic reticulum stress and apoptosis.
PDIA3 has many functions, some of these are not yet clear. Although several studies try to understand which are the PDIA3 functions in different sub-localizations, the possibility of modulating diverse functions using natural ligands is not much studied. Further studies are necessary to examine in a depth knowledge about the functionalities of this protein apparently pleiotropic. Nevertheless, it could be helpful to analyse in parallel if there are other molecules that can bind and modulate specifically PDIA3. Looking for these potential regulatory molecules in the natural compounds could be a great advantage because we can easily find them in our diets. In fact, considering that it has been reported an overexpression of PDIA3 in several types of cancer, knowing the interaction modalities and binding effects between several polyphenols and PDIA3 could be helpful for new adjuvant treatments. Moreover, natural origin of these compounds can increase the compliance of patients. The challenge is to find natural selective compounds on PDIA3 and use them such as raw extracts or as extracted and purified single molecules. In literature have been reported some compounds of synthetic origin, such as PACMA 31, LOC 14 or the biotinylated analogous of CCF642, inhibiting not only PDIA3 but also the other PDI, besides they are not without side effects [16,17,18]. Carrying out a comparative study between PDIA3 and PDIA1, I can valuate the specificity of the natural polyphenols studied, proposing a valid alternative to the synthetic compounds. Among the flavonoids, already partially studied in my first year of PhD, punicalagin has the enormous advantage of being soluble in water which facilitates the route of administration. Studying punicalagin analogues, as punicalin, could provide new inhibitors molecules with higher affinity and capacity to inhibit to the PDIA3. The compounds selected by calorimeter, fluorometric and dynamic analyses could all be used in cellular models. Tumour cell lines where the PDIA3 is overexpressed, such as SiHa, PC3, HEK293, SH-SY5Y cells can act as models to assess the biological impact of the PDIA3/polyphenol binding [19]. The identification of the pathways associated to the PDIA3/polyphenols binding can be useful to selectively control cellular processes and signalling pathways involving PDIA3 and could offer new therapeutic tools.
16- Vatolin S et al, Cancer Res. 2016 Jun 1;76(11):3340-50
17- S Xu et al, Proc Natl Acad Sci U S A, 109: 16348-53, 2012
18- A Kaplan et al, Proc Natl Acad Sci U S A, 112: E2245-52, 2015
19- The human protein atlas, (PDIA3_HUMAN)