Expression of calpain-calpastatin system (CCS) member proteins in human lymphocytes of young and elderly individuals; pilot baseline data for the CALPACENT project.

BACKGROUND: Ubiquitous system of regulatory, calcium-dependent, cytoplasmic proteases - calpains - and their endogenous inhibitor - calpastatin - is implicated in the proteolytic regulation of activation, proliferation, and apoptosis of many cell types. However, it has not been thoroughly studied in resting and activated human lymphocytes yet, especially in relation to the subjects' ageing process. The CALPACENT project is an international (Polish-Italian) project aiming at verifying the hypothesis of the role of calpains in the function of peripheral blood immune cells of Polish (Pomeranian) and Italian (Sicilian) centenarians, apparently relatively preserved in comparison to the general elderly population. In this preliminary report we aimed at establishing and comparing the baseline levels of expression of µ- and m-calpain and calpastatin in various, phenotypically defined, populations of human peripheral blood lymphocytes for healthy elderly Sicilians and Poles, as compared to these values observed in young cohort. RESULTS: We have found significant differences in the expression of both µ- and m-calpain as well as calpastatin between various populations of peripheral blood lymphocytes (CD4+, CD8+ and CD19+), both between the age groups compared and within them. Interestingly, significantly higher amounts of µ- and m-calpains but not of calpastatin could be demonstrated in the CD4+CD28- and CD8+CD28- lymphocytes of old subjects (but not in the cells of young individuals), as compared to their CD28+ counterparts. Finally, decreased expression of both calpains in the elderly T cells is not related to the accumulation of effector/memory (CD45RO+) cells in the latter, as the expression of both calpains does not differ significantly between the naïve and memory T cells, while is significantly lower for elderly lymphocytes if both populations are taken separately. CONCLUSIONS: Observed differences in the amounts of CCS member proteins between various populations of lymphocytes of young and elderly subjects may participate in the impaired proliferative activity of these cells in the elderly.

Excessive amount and activity of µ-calpain affects apoptotic machinery in chronic B-cell leukemia cells and influences the course of the disease.

B-cell Chronic Lymphocytic Leukemia (B-CLL) is the most common hematological disorder among middle-aged/elderly people in the Western countries. We have shown earlier that B-CLL cells exhibit elevated total amount and available activity of µ-calpain, belonging to a family of ubiquitous, strongly Ca-dependent proteases, involved in the control of proliferation and apoptosis. In this study we attempted to estimate a potential clinical value of µ-calpain in relation to B-CLL clinical staging in patients with extremely high lymphocytosis and studied the molecular mechanisms associating calpain activity with clinical progress of the disease. We observed significant correlations between the amounts of intracellular µ-calpain and clinical staging of the disease, with RAI stage 1 corresponding to the highest calpain amounts in the leukemic cells. There was also a positive, statistically significant correlation between the amount of µ-calpain and phosphorylated (p)ZAP-70 in B-CLL lymphocytes. Calpain activity in the B-CLL cells is associated with decreased activities of pro-apoptotic caspases -3 and -9, and reciprocally with an increased amount of anti-apoptotic Bcl-2. Together, all of these findings make calpain activity in B-CLL cells a promising target modifying the properties of these cells and facilitating therapy. Finally, the proportion of CD19+ B cells with elevated µ-calpain and pZap-70 was markedly reduced in patients after successful therapy.

Proteodynamics in aging human T cells - The need for its comprehensive study to understand the fine regulation of T lymphocyte functions.

Cellular life depends mostly on the creation, modification, interactions and destruction of proteins. This is true for every cell, including human T lymphocytes. One way these cells can ascertain the fidelity and at least partial functionality of their proteomes under constant attack of irreversible modulations (e.g., ROS- or glycation-dependent) is proteostasis. However, with cellular aging proteostasis progressively fails and proteostenosis (decreased amounts and functionalities of remaining proteins) occurs. There are several mechanisms involved in the modulation and protection of the proteome in the T cells which include mainly multiple layers of vesicle-bound and cytoplasmic proteases (e.g., lysosomal and proteasomal ones) acting mostly by degradation of obsolete and age-modified proteins. Recently it was shown that another not yet so widely known system consisting of obligatorily calcium-dependent cysteine proteases, the calpains and their inhibitor, the calpastatin serves in T cells as a dual switch, either activating or inactivating different proteins depending on intracellular conditions. Thus the proteolytic elimination of altered proteins as well as modulation of activity of those remaining leads to dynamic change of proteome composition and function (proteodynamics) in aging lymphocytes, so far in an almost unknown way. Aging T cell proteodynamics requires further comprehensive analysis of the resulting lysoproteomic patterns and their changes.

Roles of calpain-calpastatin system (CCS) in human T cell activation.

The immune response is determined by the speed of the T cell reaction to antigens assured by a state of readiness for proliferation and cytokine secretion. Proliferation, apoptosis and motion of many cell types are controlled by cytoplasmic proteases - µ- and m-calpain - and their inhibitor calpastatin, together forming the "calpain-calpastatin system" (CCS), assumed to modify their targets only upon activation-dependent cytoplasmic Ca2+ increase. Contrastingly to this notion, using quantitative real time PCR and semiquantitative flow cytometry respectively, we show here that the CCS genes are constitutively expressed, and that both calpains are constitutively active in resting, circulating human CD4+ and CD8+ lymphocytes. Furthermore, we demonstrate that calpain inhibition in the resting T cells prevents them from proliferation in vitro and greatly reduces secretion of multiple cytokines. The mechanistic reason for these effects of calpain inhibition on T cell functions might be the demonstrated significant reduction of the expression of active (phosphorylated) upstream signalling molecules, including the phospholipase C gamma, p56Lck and NFκB, in the inhibitor-treated cells. Thus, we propose that the constitutive, self-regulatory calpain-calpastatin system activity in resting human T cells is a necessary, controlling element of their readiness for complex and effective response to antigenic challenge.

Increased µ-Calpain Activity in Blasts of Common B-Precursor Childhood Acute Lymphoblastic Leukemia Correlates with Their Lower Susceptibility to Apoptosis.

Childhood acute lymphoblastic leukemia (ALL) blasts are characterized by inhibited apoptosis promoting fast disease progress. It is known that in chronic lymphocytic and acute myeloid leukemias the reduced apoptosis is strongly related with the activity of calpain-calpastatin system (CCS) composed of cytoplasmic proteases--calpains--performing the modulatory proteolysis of key proteins involved in cell proliferation and apoptosis, and of their endogenous inhibitor--calpastatin. Here, the CCS protein abundance and activity was for the first time studied in childhood ALL blasts and in control bone marrow CD19+ B cells by semi-quantitative flow cytometry and western blotting of calpastatin fragments resulting from endogenous calpain activity. Significantly higher µ-calpain (CAPN1) gene transcription, protein amounts and activity (but not those of m-calpain), with calpastatin amount and transcription of its gene (CAST) greatly varying were observed in CD19(+) ALL blasts compared to control cells. Significant inverse relation between the amount/activity of calpain and spontaneous apoptosis was noted. Patients older than 10 years (considered at higher risk) displayed increased amounts and activities of blast calpain. Finally, treatment of blasts with the tripeptide calpain inhibitors II and IV significantly and in dose-dependent fashion increased the percentage of blasts entering apoptosis. Together, these findings make the CCS a potential new predictive tool and therapeutic target in childhood ALL.

Changes in the Expression of Transcription Factors Involved in Modulating the Expression of EPO-R in Activated Human CD4-Positive Lymphocytes.

We have recently described the presence of the erythropoietin receptor (EPO-R) on CD4(+) lymphocytes and demonstrated that its expression increases during their activation, reaching a level reported to be typical for erythroid progenitors. This observation suggests that EPO-R expression is modulated during lymphocyte activation, which may be important for the cells' function. Here we investigated whether the expression of GATA1, GATA3 and Sp1 transcription factors is correlated with the expression of EPO-R in human CD4(+) lymphocytes stimulated with monoclonal anti-CD3 antibody. The expression of GATA1, GATA3 and Sp1 transcription factors in CD4(+) cells was estimated before and after stimulation with anti-CD3 antibody by Western Blot and flow cytometry. The expression of EPO-R was measured using real-time PCR and flow cytometry. There was no change in the expression of GATA1 and GATA3 in CD4(+) lymphocytes after stimulation with anti-CD3 antibody. However, stimulation resulted in the significantly increased expression of the Sp1 factor. CD4(+) lymphocytes stimulated with anti-CD3 antibody exhibited an increase in both the expression level of EPOR gene and the number of EPO-R molecules on the cells' surface, the latter being significantly correlated with the increased expression of Sp1. Sp1 is noted to be the single transcription factor among the ones studied whose level changes as a result of CD4(+) lymphocyte stimulation. It seems that Sp1 may significantly affect the number of EPO-R molecules present on the surface of activated CD4(+) lymphocytes.

Cytometric evaluation of transferrin receptor 1 (CD71) in childhood acute lymphoblastic leukemia.

Transferrin receptor 1 (CD71) is a transmembrane glycoprotein responsible for cellular iron uptake. Higher expression of CD71 has been identified as a negative prognostic marker for numerous solid tumor types and for some lymphomas. The aim of this study was to evaluate CD71 expression on acute lymphoblastic leukemia (ALL) cells and to follow its possible clinical correlations. Sixty one patients, aged 1-17 years and diagnosed with ALL, were enrolled in the study. CD71 expression was analyzed on the bone marrow blastic cells by flow cytometry. CD71 expression on the leukemic blasts was diversified; in most patients, all blastic cells showed expression of CD71, but levels of expression varied. CD71 expression was statistically higher on T-lineage leukemias. Within the B lineage ALL, a significant difference in CD71 expression existed between precursor B ALL and mature B-ALL, which showed higher CD71 expression. CD71 expression positively correlated with Hgb concentration at diagnosis. Initial risk group assessment and therapy response were not correlated with CD71 expression, although disease free and overall survival times tended to be shorter in patients with B-lineage leukemias with initial high CD71 expression.

Ex vivo measurement of calpain activation in human peripheral blood lymphocytes by detection of immunoreactive products of calpastatin degradation.

Limited proteolysis of multiple intracellular proteins by endogenous Ca-dependent cysteine proteases--calpains--is an important regulatory mechanism for cell proliferation, apoptosis etc. Its importance for cellular functions is stressed by existence of endogenous calpain inhibitors--calpastatins. The calpain-calpastatin system within living cells is in a fragile balance, which depends on both partners. The interdependence of calpain--a protease--and calpastatin--an endogenous inhibitor and at the same time a substrate for this enzyme makes any assessment of actual activity of this enzyme in the cells very difficult. In this work we made an attempt to estimate and compare the activity of calpain in human peripheral blood lymphocytes by assessing the levels of limited proteolysis of calpastatin in these cells by western blot, while at the same time the levels of calpain protein inside these cells was measured by flow cytometry. Our results indicate that it is possible to compare (semi-quantitatively) the activities of calpain in peripheral blood CD4+ and CD19+ lymphocytes from various donors that way. Preliminary results showed that calpain activity is increased in the CD4+ T cells isolated from peripheral blood of rheumatoid arthritis patients as compared to control lymphocytes. Extremely high intrinsic activity of calpain was detected in chronic lymphocytic leukemia (CD19+) cells. All this confirms the detection of immunoreactive products of calpastatin as a good maker of endogenous calpain activity.