Expression And Function Of Isoforms Of TGF-β Receptor Ⅱ In HL-60and Molt-4Cells

Under normal physiological conditions, the growth,proliferation,differentiationand apoptosis of the blood cells are regulated by a network of positive and negativecytokines. The positive cytokines can promote cells prolifertion, while the negativecytokines can inhibite cell proliferation and induce cell apoptosis. Leukemia ischaracterized as overproliferation of blood cells and the inhibition of celldifferentiation and apoptosis. The imbalance of positive and negative cytokines mayplay an important role in leukemia development.TGF-β is one of the most important negative cytokines in hematopoietic system,which can repress the proliferation of blood cells and induce the apoptosis. Theearlier result in our lab showed that lack of endogenous TGF-β expression exists inleukemia primary cells and leukemia cell lines(HL-60,Molt-4,K562) and it can becompensated by transfecting TGF-β gene into HL-60cells(a kind of leukemia cells)and exogenous TGF-β expression, which indicates that lack of TGF-β expressionmay be involved in leukemia development.Since TGF-β₁may play a role in leukemia development, the effect of TGF-βreceptor(TβR) in leukemia development, especially the expression and regulation ofTβRâ…¡, was chosen as a research focus in our lab. Our group also found for the firsttime that two TβRâ…¡ isoforms were detected among leukemia patients, named asTβRâ…¡A and TβRâ…¡B, respectively. Moreover, the expression levels of the twoisoforms in leukemia cells and normal cells were completely different. That is to say,TβR â…¡ B was mainly expressed in leukemia cells while TβR â…¡ A was mailyexpressed in normal cells.To date, it is not clear if there are some functiondifferences between the two isoforms. Based on the above, we chose leukemia cells(HL-60and Molt-4cells) as target cells,where the two isoforms of TβRâ…¡ wereoriginally express in a relatively low concentration. Then, our group cloned andover-expressed TβRâ…¡A and TβRâ…¡B in the above two cell lines. And, the effect ofTGF-β₁on the proliferation and apotosis of TβRâ…¡A or TβRâ…¡B expressionup-regulated leukemia cells and its regulation mechanism were studied.The goal of the thesis was focused on the follows:1. Expression of TβRâ…¡A or TβRâ…¡B in HL-60cells and Molt-4cells.(1) The vectors of pEFIRES-N-TβR â…¡ A and pEFIRES-N-TβR â…¡ B weretransfected into HL-60or Molt-4cells via electroporation method. And, TβRâ…¡A orTβRâ…¡B over-expressed positive leukemia cells were selected under the pressure ofantibiotics.(2) On the basis of that, expression levels of TβRâ…¡A or TβRâ…¡B in the positiveleukemia cells were determined by the methods of RT-PCR and Western Blot.2. Biological properties of TβRâ…¡ expression up-regulated HL-60or Molt-4cells.(1) The effects of TGF-β₁on the proliferation of TβRâ…¡A or TβRâ…¡B expressionup-regulated HL-60or Molt-4cells were assayed by the method of cytometry.(2) The effects of TGF-β₁on the apoptosis of TβRâ…¡A or TβRâ…¡B expressionup-regulated HL-60or Molt-4cells were assayed by the method of AO/EB usingflow cytometer.(3) The effects of TGF-β₁on the cell cycle of TβRâ…¡A or TβRâ…¡B expressionup-regulated HL-60or Molt-4cells were assayed using flow cytometer.(4) The effects of TGF-β₁on the the expression of downstream oncogene(bcl-2,c-myc,s100a6,p34),anti-oncogene(p21,p27) and several signaling moleculesin TGF-β/Smad pathway(TβRâ… ,Smad4,Smad7) in TβRâ…¡A or TβRâ…¡Bexpression up-regulated HL-60or Molt-4cells were assayed by the method of realtime PCR.(5) The effects of TGF-β₁on the expression of C-myc,Bcl-2,Smad2,Smad3,Smad4of TβRâ…¡A or TβRâ…¡B expression up-regulated HL-60or Molt-4cells wereassayed by the method of Western Blot. 3. Effect of overexpression of TGF-βRâ…¡ on HL-60induced tumor in nudemice.Transplanted tumor in nude mice was used as a model to study the tumorigenesisand proliferation of wild type HL-60cells,TβRâ…¡A and TβRâ…¡B over-expressedHL-60cells.The main results and conclusions were as follows:1. TβRâ…¡A or TβRâ…¡B over-expressed HL-60cells, TβRâ…¡A or TβRâ…¡Bover-expressed Molt-4cells were successfully selected and used as cell models.Theywere named as follows: HL-60/pEFIRES-N cells (pEFIRES-N empty vectortransfected HL-60cells),HL-60/TβRâ…¡A cells(pEFIRES-N-TβRâ…¡A recombinantplasmid transfected HL-60cells),HL-60/pEFIRES-P cells(pEFIRES-P emptyvector transfected HL-60cells),HL-60/TβRâ…¡B cells(pEFIRES-P-TβRâ…¡Brecombinant plasmid transfected HL-60cells), Molt-4/pEFIRES-N cells(pEFIRES-N empty vector transfected Molt-4cells),Molt-4/TβRâ…¡A cells(pEFIRES-N-TβR â…¡ A recombinant plasmid transfected Molt-4cells),Molt-4/pEFIRES-P cells(pEFIRES-P empty vector transfected Molt-4cells) andMolt-4/TβRâ…¡B cells(pEFIRES-P-TβRâ…¡B recombinant plasmid transfected Molt-4cells).2. Cell proliferation assayed by cytometry was as follows: Compared withrespective reference, the proliferation inhibiton of HL-60/TβRâ…¡A cells by TGF-β₁in a concentration range of0-12ng/ml was enhanced and was time-and dose-dependent, while that of HL-60/TβRâ…¡B cells was not significantly inhibited;Similarly, the proliferation of Molt-4/TβRâ…¡A cells was more strongly inhibited byTGF-β₁than that of Molt-4/TβRâ…¡B cells. In a concentration range of0-20ng/ml,the proliferation inhibiton of Molt-4/TβRâ…¡A cells by TGF-β₁was enhancedcompared with respective reference and the inhibition was time-and dose-dependent, too.3. Apoptosis assay result was as follows: Compared with respective reference,the apoptosis of HL-60/TβRâ…¡A cells by TGF-β₁in a concentration range of0-12ng/ml was enhanced and was time-and dose-dependent. Under24h effect of10 ng/ml TGF-β₁, the total apoptosis rate of HL-60/TβRâ…¡A cells was2.34%andhigher than that of HL-60/TβRâ…¡B cells(0.08%) and HL-60cells(0.06%); Under96h effect of10ng/ml TGF-β₁, there was a higher apoptosis rate(28.26%) inHL-60/TβR â…¡ A cells than that(21.44%) in HL-60/TβR â…¡ B cells or HL-60cells(6.09%). Similarly, the apoptosis of Molt-4/TβRâ…¡A cells by TGF-β₁in aconcentration range of0-20ng/ml was enhanced and was time-and dose-dependent.Under24h effect of12ng/ml TGF-β₁, the total apoptosis rate of Molt-4/TβRâ…¡Acells was2.98%and higher than that of Molt-4/TβRâ…¡B cells(1.8%) or Molt-4cells(0.16%); Under72h effect of12ng/ml TGF-β₁, the total apoptosisrate(74.63%) of Molt-4/TβRâ…¡A cells was significantly higher than that(48.82%) ofMolt-4/TβRâ…¡B cells or that(17.88%) of Molt-4cells.4. Flow cytometer assay result showed that under the effect of10ng/ml TGF-β₁for24-96h, the ratio of HL-60/TβRâ…¡A cells in S-phase was decreased and that ofHL-60/TβRâ…¡A cells in G1-phase was increased. And, the differences betweenHL-60/TβRâ…¡A cells and the other cells lines became more significant when theeffect time was extended. Under24h effect of TGF-β₁, the ratio of HL-60/TβRâ…¡Acells in S-phase was47.51%, which was a little lower than that of HL-60cells(55.46%) and that of HL-60/TβRâ…¡B cells (51.92%); Under96h effect ofTGF-β₁, the ratio of HL-60/TβRâ…¡A cells in S-phase was20.20%, which wassignificantly lower than that of HL-60cells(58.35%) and that of HL-60/TβRâ…¡Bcells (56.22%).Similarly, under the effect of12ng/ml TGF-β₁for24-96h, the ratioof Molt-4/TβRâ…¡A cells in S-phase was decreased and that of Molt-4/TβRâ…¡A cellsin G1-phase was increased. Under24h effect of TGF-β₁, the ratio of Molt-4/TβRâ…¡A cells in S-phase was32.58%, which was a little lower than that of Molt-4cells(41.77%) and that of Molt-4TβRâ…¡B cells (36.83%). Under72h effect ofTGF-β₁, the ratio of Molt-4/TβRâ…¡A cells in S-phase was25.64%, which wassignificantly lower than that of Molt-4cells(49.87%) and that of Molt-4TβRâ…¡Bcells (34.01%).5. Real time PCR assay result showed that under96h effect of10ng/ml TGF-β₁, the expression of ongogene(bcl-2,c-myc,p34) in HL-60/TβRâ…¡A cells wasdown-regulated significantly while that of antiongogene p21was greatlyup-regulated. In HL-60/TβRâ…¡B or HL-60cells, bcl-2and c-myc was slightlydown-regulated and the expression of p21and p34remained constant under the sameconditions. The expression change of other genes(TβRâ… ,Smad4,Smad7,s100a6,p27) had not detected in HL-60/TβRâ…¡A cells,HL-60/TβRâ…¡B cells or HL-60cells.Also, under72h effect of12ng/ml TGF-β₁, the expression of ongogene(c-myc)among Molt-4/TβRâ…¡A and Molt-4/TβRâ…¡B cells was down-regulated significantlywhile that of antiongogene (p21and p27) was greatly up-regulated; and, the changelevels of c-myc,p27and p21in Molt-4/TβRâ…¡A cells were much more significantthan that in Molt-4/TβRâ…¡B cells. And the expression change of c-myc,p27and p21in Molt-4cells was not detected. Also, the expression change of other genes(TβRâ… ,Smad4,Smad7) had not detected in Molt-4/TβRâ…¡A cells, Molt-4/TβRâ…¡B cellsand Molt-4cells. In addition, the expression of bcl-2,s100a6,p34in all Molt-4celllines had not detected by the method of real time PCR.6. Western-Blot assay result showed that under96h effect of10ng/ml TGF-β₁,the expression of Bcl-2and C-myc among HL-60/TβRâ…¡A cells was greatlydown-regulated, which was not observed among HL-60/TβRâ…¡B cells under thesame conditions.The expression change of Smad2,Smad3and Smad4in HL-60/TβRâ…¡A cells was not detected. Also, under72h effect of12ng/ml TGF-β₁, theexpression of Bcl-2and C-myc among Molt-4/TβRâ…¡A and Molt-4/TβRâ…¡B cellswas down-regulated to different degrees and the change among Molt-4/TβRâ…¡Acells was more significant than that among Molt-4/TβRâ…¡B cells. In addition, theexpression change of Smad2, Smad3and Smad4among Molt-4/TβR â…¡ A orMolt-4/TβRâ…¡B cells was not detected.7. The result of nude mice experiments showed: tumorigenesis time periods ofHL-60/pEFIRES-N cells(control),HL-60/pEFIRES-P cells(control),HL-60/TβRâ…¡A cells(experimental group) and HL-60/TβRâ…¡B cells(experimental group) were8.25d,8.88d,12.38d and10.25d respectively. The tumorigenesis time of theexperiment group was significantly extended compared with that of the control. After inoculation for22d, the average volumes of tumors induced by the above fourcell lines were5.39±2.67cm3,5.15±2.87cm3,1.18±1.12cm3and3.31±2.37cm3respectively. The average volumes of tumors of the experiment group wassignificantly reduced compared with that of the control(p＜0.05).And the averageweigh of tumors induced by the above four cell lines were3.54±1.84g,3.46±1.61g,0.98±0.74g and2.15±1.43g respectively. The weight of the induced tumors of theexperiment group was significantly decreased compared with that of the control(p＜0.05).And, HL-60/TβRâ…¡A cells' tumorigenic ablity in nude mice was muchweaker than HL-60/TβRâ…¡B cells.Conclusion: TβR â…¡ A and TβRâ…¡B displayed a function difference.HL-60/TβRâ…¡A and Molt-4/TβRâ…¡A cells became more sensitive to TGF-β₁and theinhibition of their proliferation and the apoptosis induced by TGF-β₁were moresignificant than the effects on HL-60/TβRâ…¡B and Molt-4/TβRâ…¡B cells. And, TβRâ…¡B was majorly expressed in leukemia cells while TβRâ…¡A was majorly expressedin hematopoietic stem cells. Based on the above, it was assumed that the abnormalexpression of the two isoforms of TβRâ…¡ may be involved in the development ofleukemia.