Badanie ekspresji podtypów receptora somatostatynowego w ludzkich guzach endokrynnych

• Authors: Hanna Pisarek

Title variants

EN

Investigation of somatostatin receptor subtypes expression in human endocrine tumors

• Languages of publication: PL

Abstracts

EN

Somatostatin (SST) – a hypothalamic polipeptide discovered in 70-ies of last century, is widely distributed in the central and peripheral nervous system, the pituitary gland and other tissues such as the pancreas, adrenals, intestine, kidneys, prostate, placenta and the cells of immune system. It exerts a number of different endo- and exocrine biological effects, predominantly of inhibitory nature. Somatostatin inhibits hormones secretion (GH, TSH, insulin, glucagon, gastrin, ghrelin, VIP). One of the most encouraging aspects of somatostatin effects, particularly in the context of tumor diseases therapy, is its antiproliferative action. It acts as both cytostatic (growth inhibition) as well as cytotoxic (apoptosis induction) agent. It inhibits also the angiogenesis process. Somatostatin as well as its synthetic analogs act via specific receptors which are present on the surface of the target cells. These receptors are glycoproteins and belong to a group of seven transmembrane domains linked with the G protein. Five subtypes of the SST receptor have been identified i.e. SSTR 1-5 with two splicing variants (2A and 2B) of the type 2 receptor. Recently, the new two variants of SSTR 5 (SSTR 5B and SSTR 5C) have been identified. The highly variable expression of SSTR subtypes in pituitary adenomas and neuroendocrine tumors of gastrointestinal tract, may partially explain why some tumors of this type do not respond to therapeutic action. This kind of therapy currently applies long-acting somatostatin analogs like octreotide or lanreotide which act mainly via SSTR 2 and SSTR 5 subtypes of somatostatin receptors. The studies describing the expression of somatostatin receptor subtypes in other endocrine tumors like thyroid and adrenal gland tumors are still rare and often confusing. They applied mainly to the molecular biology methods (mainly PCR). Immunohistochemical investigations are not numerous. Thus in my investigations I have taken a trial of immunohistochemical estimation of somatostatin receptor subtypes (including 2A and 2B SSTR isoforms) in surgically treated human adrenal tumors, thyroid tumors, pituitary adenomas and neuroendocrine tumors. In case of thyroid tumors, additionally molecular biology method was used (Real-Time PCR) to correlate the results obtained with both techniques. During my pituitary adenomas investigations, I could observed the distribution of somatostatin receptor subtypes in plurihormonal adenomas in order to answer the question if the immunopositivity of GH or ACTH is linked or not to more abundant expression of particular SSTR subtypes. For the first time, I could described this kind of correlation. The pattern of SSTR immunostaining in pituitary adenomas, estimated according to the frequency of appearance and expressed in percentage rate was made. Being based on the obtained results, I have drown the following conclusions: 1. The adrenal gland tumors, thyroid tumors, pituitary adenomas and neuroendocrine tumors exhibit the somatostatin receptor subtypes expression in a varied manner being specific in each case. There are variable levels both in different group of tumors as well as in the tumors of the same type. 2. In the adrenal gland tumors SSTR 5 is the dominant subtype of somatostatin receptor, SSTR 1 is expressed at the lower level. 3. Subtype SSTR 1 is the dominant form in the thyroid gland tumor and hyperplasia. 4. It was demonstrated the 100% of correlation between immunohistochemical - IHC and RT-PCR methods for SSTR 5. 5. The expression of all somatostatin receptor subtypes (SSTR 1-5) in pituitary adenomas depends on the hormonal phenotype of the tumor: • in somatotropinomas dominate two subtypes of receptor: SSTR 5 (88,8%) and SSTR 1 (77,8%), • in all prolactinomas SSTR 2B, SSTR 3 and SSTR 5 were found, gonadotroph adenomas demonstrated the low level of SSTR, with the strongest expression for SSTR 3 (27,3%) and SSTR 2B (22,7%), • in all of pituitary adenomas secreting ACTH – corticotropinomas, SSTR 2A was found and in 80% of cases the expression of SSTR 1 and SSTR 3 was detected, • the enhanced immunpositivity for SSTR 1 and SSTR 5 in plurihormonal pituitary adenomas was demonstrated for the first time; the expression of these somatostatin receptor subtypes does not depend on GH secretion by tumor’s cells. 6. In the neuroendocrine tumors the subtypes SSTR 1 (58,8%) and SSTR 5 (52,9%) are most often expressed, however the subtypes 3 and 2A were found in 41,2% and 33,3% of cases respectively. 7. SSTR 1-5 characterized membrane and cytoplasmic distribution in the cells of tumors. 8. The results presented in my studies confirm the high utility of immunohistochemical method to investigate the expression of somatostatin receptor subtypes.

PL

Somatostatyna (SST) - podwzgórzowy polipeptyd odkryty w latach 70-tych ubiegłego wieku, szeroko występuje w neuronach centralnego i obwodowego układu nerwowego, w przysadce, a takŜe w trzustce, nadnerczach, przewodzie pokarmowym, nerkach, prostacie, łoŜysku oraz w komórkach układu immunologicznego. Wywiera szereg róŜnorodnych efektów biologicznych: endo- i egzokrynnych, polegających głównie na hamowaniu sekrecji róŜnych hormonów (hormonu wzrostu -GH, tyreotropiny, insuliny, glukagonu, gastryny, ghreliny, VIP), a takŜe zmniejszeniu proliferacji komórkowej. To ostatnie działanie SST jest jednym z najbardziej interesujących efektów SST, zwłaszcza w aspekcie prób leczenia chorób nowotworowych. Somatostatyna działa zarówno cytostatyczne (hamowanie wzrostu), jak i cytotoksyczne (indukcja apoptozy), a takŜe hamuje angiogenezę. Somatostatyna, a takŜe jej długo działające syntetyczne analogi, wywierają swoje działanie za pośrednictwem specyficznych receptorów obecnych na powierzchni komórek docelowych. Mają one charakter glikoproteinowy i wiadomo, Ŝe naleŜą do grupy receptorów błonowych posiadających siedem obszarów transmembranowych i związanych z białkiem G. Zdefiniowano pięć podtypów receptora SST: SSTR 1-5. Podtyp SSTR 2 posiada dwie izoformy: 2A i 2B, a ostatnio zidentyfikowano takŜe dwa nowe warianty podtypu SSTR 5: SSTR 5B i SSTR 5C. Receptory somatostatynowe występują nie tylko w tkankach prawidłowych, lecz takŜe w guzach nowotworowych, co pozwala przewidzieć pozytywną odpowiedź na stosowanie analogów SST. DuŜa róŜnorodność ekspresji podtypów SSTR 1-5 w gruczolakach przysadki, a takŜe w guzach neuroendokrynnych przewodu pokarmowego moŜe częściowo wyjaśniać dlaczego w niektórych guzach tego typu, obserwuje się brak odpowiedzi na działanie analogów somatostatyny o przedłuŜonym działaniu, takich jak oktreotyd i lanreotyd, wiąŜących się głównie z podtypem receptora 2 i 5. Prace na temat występowania receptorów somatostatynowych w nowotworach innych gruczołów dokrewnych, takich jak nowotwory tarczycy i nadnerczy są nieliczne i prezentują sprzeczne wyniki. Badania te były jednak prowadzone głównie metodą łańcuchowej reakcji polimerazy (PCR), natomiast mniej badań przeprowadzono z uŜyciem metody immunohistochemicznej. Dlatego teŜ w swoich badaniach podjęłam próbę immunohistochemicznej oceny ekspresji podtypów receptora somatostatynowego SSTR 1-5 (z uwzględnieniem izoform SSTR 2A i 2B) w nowotworach tych narządów, a prezentowana praca jest podsumowaniem obserwacji własnych na tle dotychczasowego piśmiennictwa. W przypadku chorób tarczycy, równolegle wykonane zostały takŜe badania na poziomie molekularnym (RT-PCR) i przeprowadzono ocenę zgodności wyników uzyskanych tymi dwiema metodami. Omawiając występowanie SSTR w gruczolakach przysadki, po raz pierwszy dokonałam opisu dystrybucji SSTR w guzach wielohormonalnych tego gruczołu, odpowiadając na pytanie czy fakt współwystępowania GH lub ACTH w guzie ma związek ze zwiększoną ekspresją danego podtypu receptora. Na podstawie procentowej częstości występowania, określiłam wzory immunoekspresji SSTR 1-5 w gruczolakach przysadki. Otrzymane wyniki upowaŜniają do formułowania następujących wniosków: 1. Guzy nadnerczy, tarczycy, przysadki oraz guzy neuroendokrynne wykazują ekspresję podtypów receptora somatostatynowego SSTR 1-5 w sposób bardzo zróŜnicowany i specyficzny dla danego przypadku. Istnieją róŜnice w ekspresji SSTR 1-5 pomiędzy guzami róŜnych typów, jak równieŜ wśród guzów tego samego rodzaju. 2. W guzach nadnerczy dominuje SSTR 5, w mniejszym stopniu występuje SSTR 1. 3. Podtyp SSTR 1 receptora somatostatynowego jest dominującym podtypem w rakach i w łagodnych rozrostach gruczołu tarczowego. 4. Wykazano 100% zgodność pomiędzy metodą immunohistochemiczną - IHC i techniką RT-PCR dla SSTR 5. 5. Ekspresja podtypów receptora somatostatynowego w gruczolakach przysadki zaleŜy od fenotypu hormonalnego guza: • w guzach somatotropowych dominują dwa podtypy receptora: SSTR 5 (88,8%) i SSTR 1 (77,8%), • we wszystkich guzach prolaktynowych stwierdzono obecność SSTR 2B, SSTR 3 i SSTR 5, • w gruczolakach gonadotropowych stwierdzono niską ekspresję SSTR, wynoszącą maksymalnie dla SSTR 3 - 27,3%, a dla SSTR 2B - 22,7%, • we wszystkich gruczolakach przysadki wydzielających ACTHcorticotropinoma stwierdzono ekspresję SSTR 2A, a występowanie SSTR 1 i SSTR 3 w 80% przypadków. • po raz pierwszy wykazano w wielohormonalnych gruczolakach przysadki (adenoma plurihormonale) zwiększoną immunopozytywność SSTR 1 i SSTR 5, a ekspresja tych podtypów nie była związana z sekrecją hormonu wzrostu przez komórki guza, 6. W guzach neuroendokrynnych (NET) dominowały podtypy: SSTR 1 (58,8%) i SSTR 5 (52,9%), natomiast SSTR 3 stwierdzono w 41,2% a SSTR 2A w 33,3% przypadków. 7. SSTR 1-5 charakteryzują się błonową lub cytoplazmatyczną dystrybucją w komórce. 8. Przedstawione w pracy wyniki potwierdzają wysoką uŜyteczność immunohistochemicznej metody badania ekspresji receptorów somatostatynowych.

Keywords

EN

Guzy endokrynne; somatostatyna

Discipline

• MEDICINE: MEDICINE

• Journal: Folia Medica Lodziensia
• Year: 2009
• Volume: 36
• Issue: 1
• Pages: 5-71

Contributors

author

Hanna Pisarek

• Zakład Neuroendokrynologii Uniwersytet Medyczny w Łodzi

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• Document Type: paper