The Effect of Temperature on Recombinant Human Granulocyte Colony Stimulating Factor Production by Pichia pastoris Expression System

Email: yuliawati.goli@gmail.com ABSTRACT Granulocyte colony stimulating factor (G-CSF) is a haematopoetic growth factor that functions as specific stimulator of the survival, proliferation, and differentiation of precursor cells of the neutrophilic granulocyte cell lineage as well as an activator of mature neutrophil function. The main objective of this work is to compare the effect of different temperature on the production of extracellular recombinant G-CSF in Pichia pastoris. Cells were cultured for 72h in baffled shake-flasks at 20°C, 25°C, and 30°C in two different medium; buffered glycerol/methanol-complex medium (BMGY/BMMY) and buffered minimal glycerol/methanol (BMGH/BMMH) after methanol induction every 12h. Expressed recombinant hG-CSF in the methylotrophic yeast P. pastoris was analyzed with SDS-PAGE. The 23 kDa protein was secreted into the culture supernatant when induced with methanol. Production of recombinant G-CSF protein in P. pastoris at 30°C at 48h incubation after methanol induction every 12h is the highest in both complex and minimum medium.


INTRODUCTION
Granulocyte colony-stimulating factor (G-CSF) also known as colony-stimulating factor 3 (CSF 3) is a colony-stimulating factor hormone.G-CSF is a glycoprotein, growth factor and cytokine produced by a number of different tissues to stimulate the bone marrow to produce granulocytes and stem cells.G-CSF then stimulates the bone marrow to release them into the blood.G-CSF also stimulates the survival, proliferation, differentiation, and function of neutrophil precursors and mature neutrophils.The recombinant human G-CSF synthetized in an Escherichia coli expression system is called filgrastim (Neupogen).Another form of recombinant human G-CSF called lenograstim is synthesized in Chinese Hamster Ovary cells (CHO cells).G-CSF is produced by endothelium, macrophages, and a number of other immune cells.This natural human glycoprotein exists in two forms, a 174-and 180-amino-acid-long protein of molecular weight 18671.65 dalton and 19600 dalton.The more abundant and more active 174-amino acid form has been used in the development of pharmaceutical products by recombinant DNA (rDNA) technology (Hongbao et al, 2011).
Human granulocyte-colony stimulating factor (hG-CSF) cDNA was expressed in the methylotrophic yeast Pichia pastoris under the control of the alcohol oxydase (AOX1) promoter [Bahrami et al (2007), Bahrami et al (2008)].Bahrami et al. (2007) was using pPIC9 vector secretion constructed as an expression vector for hG-CSF.Higher levels of hG-CSF was obtained using a P. pastoris Mut+ (methanol utilization fast) phenotype.They also investigated the effects of environmental factors such as temperature and pH on the P. pastoris cell growth and hG-CSF production during fermentation.This study using pPICZαA vector as an expression vector for G-CSF.The host cell using P. pastoris SMD1168H.Cereghino and Cregg (2000) state that P. pastoris have been developed as a highly popular expression system for the production of variety of therapeutic proteins.P. pastoris used preferred over eukaryotic expression systems because of its efficiency, simplicity and affordability.This host can typically be grown to high cell density and is a potent expression system with great capability to secrete recombinant proteins into the medium (Cereghino et al. 2002).One of the most important features of yeast expression systems is their ability to perform eukaryotic posttranslational protein modifications, such as Nand O-glycosylation, disulfide bond formation, and oligomerization.The majority of therapeutic proteins display one or more posttranslational modifications (PTMs), and these PTMs are often essential for the functionality of these proteins (Corchero et al. 2012) Recombinant protein in this study using P. pastoris as host cell which has been integrated with gcsf gene.This gene was inserted with the c-myc tag and six histidine tag (6× His) at Cterminal.It was inserted into pPICZαA vector (Invitrogen).For extracellular secretion of recombinant protein, some commercial expression vectors contain a sequence encoding the secretion an epitope tag for affinity purification or detection of the recombinant protein such as 6×His, FLAG, HA, and c-myc tags are generally included in frame with the gene of interest (Çelik, and Çalık, 2012).
Most processes with P. pastoris are run at a temperature of 30°C, which is optimum for growth.By decreasing growth temperature from 30 to 20°C, a 3-fold increase in specific recombinant protein productivity was obtained in chemostat cultures of P. pastoris, which was accompanied by a reduced flux through the TCA-cycle, reduced levels of proteins involved in oxidative stress response and lower cellular levels of molecular chaperones (Çelik, and Çalık, 2012).
Fickers (2014) reviewed that bioprocess parameters such as medium composition, pH, temperature, aeration rate, induction and feeding strategies are of utmost (very) importance since it affects directly the production yield.Those parameters vary according to the genotype of the producing strain and/or the recombinant protein.However, there are some guidelines that allow high productivity yields.The main objective of this work is to compare the effect of different temperature in two kinds medium on the production of extracellular recombinant G-CSF in P. pastoris SMD1168H.This study using pPICZαA vector as an expression vector for G-CSF.Expressed recombinant Pichia strain is a strain that has been inserted gene recombinant gcsf-cmyc.The gene is a synthetic gene which is the result of the construction of recombinant genes our previous study.

Yeast strain and Plasmid
The EasySelect ® Pichia expression system was used for genetic engineering experiments.The expression vector pPICZa and host cells of P. pastoris SMD1168H containing the AOX1 promoter, which allows rapid growth on methanol as the carbon source, were used for heterologous protein expression of G-CSF.The recombinant P. pastoris strain SMD1168H which has been inserted gene gcsf-cmyc was obtained from our previous study.

Recombinant
protein (extracellular product) was analyzed using SDS-PAGE and BCA methods.The BCA Protein Assay Kit (Pierce, Bonn, Germany) was used according to the manufacturer's instructions using test-tube procedure.BCA's method was used with serum bovine albumin as protein standard.Cultures protein were harvested by centrifugation (10.000rpm, 15min, 4°C).Proteins were precipitated from cell-free supernatant samples by TCA solution (trichloro acetic acid) (Florens & Washburn, 2008).Sample results of TCA then resuspended in phosphate buffer at 25µL.Its used to BCA assay as much 12.5µL sample for the measurement.Then sample added 8× cv BCA working reagent and incubated at 37 for 30min.Once it is added to 500uL ddH2O and read at a wavelength of 562nm.

RESULT AND DISCUSSION
A recombinant P. pastoris strain which can express protein G-CSF-cmyc was constructed in our previous study.Briefly, the gcsf-cmyc gene bearing pPICZαA plasmid was introduced into P. pastoris strain SMD1168H to generated the SMD1168H/G-CSF-cmyc strain.The recombinant G-CSF-cmyc expression was confirmed by SDS PAGE and Western Blot analysis, as analyzed in other part of this research.Appeared on SDS PAGE as a protein of ~23 kDa (which corresponds with a theoretical molecular weight of 23 kDa).Cos et al. (2005) and Li et al. (2007) stated that heterologous protein expression under control of pAOX1 allows for the design of defined controlled high cell density cultivation strategies for heterologous protein production, described in two main phases.First phase is to generate biomass utilizing carbon sources that lead to a high substrate-biomass yield, such as glycerol; the cells are grown until glycerol is depleted.The second phase, in the presence of methanol, is for induction of foreign protein expression.Optimization of cultivation processses usually involve intermediate cultivation phase, where both carbon sources are present.
To optimize condition for the expression of G-CSF, Pichia transformant were cultured for 72h in baffled shake-flasks at, 20°C, 25°C, and 30°C in two different medium; buffered glycerol/ methanol-complex medium (BMGY/ BMMY) and buffered minimal glycerol/ methanol (BMG/BMM).Every treatment was done in triplicate.Recombinant yeasts grew much faster and reach a higher cell density in the complex medium BMMY (OD600 of 24.8 to 25.77) and in the minimal medium BMM (OD600 of 16.6 to 17.39) (Table I).The highest OD on complex medium obtained in temperature 30°C, while in minimal medium in temperature 25°C.The rate of methanol conversion determines the available energy and carbon for maintenance, cell growth, product formation and product transport into the media.Overall productivities for cell mass and HSA (human serum albumin) showed similar dependence on methanol concentration as the specific rates (Kupcsulik & Sevella, 2004).
The environmental condition, e.g.temperature and fermentation processes have close correlation with the cell growth, the internal secretion pathway machinery, the secretion levels of proteins, and their stability in the medium.Another parameter is media composition.The optimal culture medium depends on many factors, including host metabolism, potential inhibitory products, target protein, ect.(Hou et al., 2012).P. pastoris considrable to to produce heterologous proteins.Production of heterologous proteins consisted of two phase; biomass production phase and recombinant protein production phase.In the first phase, as the sole carbon source glycerol is initially added to medium.During this phase, biomass is accumulated, but the gene expression of heterologous proteins is completely repressed.In the second phase, after the initial depletion of glycerol, there is a transition period in which glycerol is added to the culture at a limiting rate (nutritional stress).In many production heterologous protein with P. pastoris as a host cell, complex medium is required for growth and induction of protein expression (Aizemberg et al., 2011).
Complex medium is used for both growth and induction of protein expression in the field of recombinant protein production from P. pastoris.Complex media are excellent for providing the correct chemical environment required for Pichia cell growth, they have some limitations when considering larger-scale and industrial fermentations.The use of minimal media is expected to reduce production costs for a larger scale and industrial scale fermentation.
G-CSF was secreted from Pichia transformant after methanol induction every 12h at different temperature (20, 25, and 30°C) for 72h.Protein analysis was done after TCA precipitation of culture supernatant on 12% SDS-PAGE and visualized by commasie blue (Figure 1).
Strategies of combination cultivationlevel (in complex and minimal medium towards temperature) are effective to obtained intact recombinant protein, it was produced by P. pastoris with minimum proteolytic degradation.The work described in this section demonstrates the necessity to optimize production/ cultivation process at all levels, not only to achieve maximum growth and protein production, but also to obtain maximal amounts of the desired protein in an intact and bioactive form (Aizemberg et al., 2011).Most of the processes of recombinant protein production by P. pastoris are performed at 30°C which is the optimal growth temperature (Fickers, 2014) (Figure 1 and Table II) in complex medium the yield of recombinant protein in temperature condition 30°C at 48h is the highest than other condition  minimum medium approximately 6.31 to 23.36mg/L.Chien (2010) reported that gene expression in the protease resistant strain of yeast (SMD1168) the total recombinant G-CSF protein in shaking flask medium was estimated as 15mg/L.Expressed mGM-CSF in GS115, Jacobs et al. (2010) and Saeedina ( 2008) also reported have a final yield of ~18mg/L and 3.1mg/L respectively.

CONCLUSION
Recombinant hG-CSF produced in the methylotrophic yeast Pichia pastoris analyzed with SDS-PAGE.Protein was secreted into the culture supernatant when induced with methanol, the proteins have a size of 23 kDa.Production of recombinant G-CSF protein in P. pastoris at 30°C at 48h incubation after methanol induction every 12h is the highest in both complex and minimum medium.

Table I .
Optical Density (OD600) of Pichia pastoris Culture in BMMY and BMM at 72h.