| 1. |
- Nagy, Noemi
(författare)
-
Expression and function of the small immune adaptor protein SAP
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Epstein-Barr virus (EBV) carrier state is widespread in humans. Primary infection can cause infectious mononucleosis (IM) that presents with variable clinical severity, but almost always subsides. For 50% of boys with a rare hereditary immunodeficiency, X-linked lymphoproliferative disease (XLP), primary infection with E13V has a fatal course. In addition, XLP patients have elevated (200 times) risk for development of lymphomas. The underlying cause of the syndrome is lack of the function of a protein SAP, due to mutations of the encoding gene named also DSHP or SH2DIA. SAP binds to a group of cell surface proteins belonging to the SLAM-family. We found an increase of SAP in T and NK cells after their activation. This correlated well with the inadequacy of cell mediated immune functions in the affected individuals, indicating the importance of SAP. SAP was absent in B cells infected with EBV and in the established lymphoblastoid cell lines (LCL), in SAC+IL-2 or CD40L+IL-4 activated B cells. EBV carrying - but not EBV negative - Burkitt lymphoma (BL) lines with the Type I EBV expression pattern were SAP positive. The type III lines had no SAP. The difference between the EBV negative BLs and the group I EBV positive lines is the first marker that distinguishes these 2 groups. Our results suggest that CD40 ligation can be the physiological signal for SAP down-regulation in B cells. We have also detected SAP in 5 EBV negative cell lines derived from Hodgkin's disease. In the continuation of our studies we focused our attention on the high incidence of lymphoma development in the XLP patients. Since lymphomas appear with high frequency even in EBV negative XLP patients, we considered that in addition to the immunological defect, the absence of SAP may lead to an intrinsic B cell dysfunction. This could possibly affect apoptosis/cell cycle control/DNA repair. We identified SAP as one of the targets of p53. We used a temperature sensitive p53 system and a panel of cell lines with endogenous wt p53. With the help of chromatin immunoprecipitation assay (ChIP) we have proven the functionality of one of the 2 possible p53 binding sites. DNA damage induced by ã-irradiation, induced SAP expression in primary T cells. Induction of SAP by p53 was tissue specific. Our results suggest that SAP contributes to the execution of some p53 functions. We have introduced SAP by retroviral transduction to various cell lines and found that SAP elevated the sensitivity of cells to DNA damage. This was established by cell survival and colony formation assays. We also showed that the proportion of apoptotic cells was higher in the SAP positive populations. Thus SAP has a pro-apoptotic role. We found that in activated T cells the SAP level is increased in the late phase of activation. The high levels of SAP showed a negative correlation with cell proliferation. Furthermore, clones of the T-ALL cell line with low and high SAP expression showed that the latter are more prone to activation induced cell death. Altogether, we have shown that absence of SAP function modifies cell proliferation / cell survival and by this we have introduced a new dimension to SAP and to XLP. Loss of this function can contribute to the maintenance of over-activated, proliferating T cells in the fatal IM and also to the development of lymphomas.
|
|
| 2. |
- Nagy, Noemi, et al.
(författare)
-
The apoptosis modulating role of SAP (SLAM associated protein) contributes to the symptomatology of the X linked lymphoproliferative disease
- 2009
-
Ingår i: Cell Cycle. - : Landes Bioscience. - 1538-4101 .- 1551-4005. ; 8:19, s. 3086-3090
-
Tidskriftsartikel (refereegranskat)abstract
- Deletion or mutation of the SH2D1A gene located at Xq25 is responsible for the development of the X-linked lymphoproliferative disease, XLP. Primary infection of the affected individuals with EBV leads to fulminant and often fatal infectious mononucleosis, FIM. Moreover, they run a 200 fold elevated risk for lymphoma development. Due to the critical role of the immune response for the outcome of EBV infection and the detection of EBV genomes in several malignancies, XLP studies have been mainly focused on the immunological aspects. The involvement of SAP in the apoptotic machinery provides a further aspect in the complex syndrome of XLP. Functional impairment of SAP leads to defective apoptotic responses. Activation induced apoptosis plays a pivotal role in the termination of the lymphocyte proliferation in IM. This mechanism is inefficient in XLP patients. In addition, in the absence of SAP, lymphoma development may be promoted by the illegitimate survival of lymphocytes with damaged DNA that would be normally eliminated by apoptosis.
|
|
| 3. |
- Nagy, Noémi, et al.
(författare)
-
The proapoptotic function of SAP provides a clue to the clinical picture of X-linked lymphoproliferative disease
- 2009
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:29, s. 11966-11971
-
Tidskriftsartikel (refereegranskat)abstract
- Deletion or mutation of the SAP gene is associated with the X-linked lymphoproliferative disease (XLP) that is characterized by extreme sensitivity to Epstein-Barr virus (EBV). Primary infection of the affected individuals leads to serious, sometimes fatal infectious mononucleosis (IM) and proneness to lymphoma. Our present results revealed a proapoptotic function of SAP by which it contributes to the maintenance of T-cell homeostasis and to the elimination of potentially dangerous DNA-damaged cells. Therefore, the loss of this function could be responsible for the uncontrolled T-cell proliferation in fatal IM and for the generation of lymphomas. We show now the role of SAP in apoptosis in T and B lymphocyte-derived lines. Among the clones of T-ALL line, the ones with higher SAP levels succumbed more promptly to activation induced cell death (AICD). Importantly, introduction of SAP expression into lymphoblastoid cell lines (LCL) established from XLP patients led to elevated apoptotic response to DNA damage. Similar results were obtained in the osteosarcoma line, Saos-2. We have shown that the anti-apoptotic protein VCP (valosin-containing protein) binds to SAP, suggesting that it could be instrumental in the enhanced apoptotic response modulated by SAP.
|
|
