Mitogenic factors present in serum but not in plasma

Identification of the primary ciliary proteins IFT38 and IFT144 to enhance serum-mediated YAP activation and cell proliferation

Primary cilia are essential cellular antennae that transmit external signals into intracellular responses. These sensory organelles perform crucial tasks in triggering intracellular signaling pathways, including those initiated by G protein-coupled receptors (GPCRs). Given the involvement of GPCRs in serum-induced signaling, we investigated the contribution of ciliary proteins in mitogen perception and cell proliferation. We found that depletion of cilia via IFT88 silencing impaired cell growth and repressed YAP activation against serum and its mitogenic constituents, namely lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P). To identify the key player of serum mitogen signaling, a mutant cell line library with 30 ablated individual ciliary proteins was established and screened based on YAP dephosphorylation and target gene induction. While 9 of them had altered signaling, ablation of IFT38 or IFT144 led to a particularly robust repression of YAP activation upon LPA and S1P. The deficiency of IFT38 and IFT144 attenuated cell proliferation, as corroborated in either 2-dimensional cultures or tumor spheroids. In subcutaneous skin melanoma patients, expression of IFT38 and IFT144 was associated with unfavorable outcomes in overall survival. In conclusion, our study demonstrates the involvement of ciliary proteins in mitogen signaling and identifies the regulatory roles of IFT38 and IFT144 in serum-mediated Hippo pathway signaling and cellular growth.

Human Serum for Culture of Articular Chondrocytes

In the field of cell and tissue engineering, culture expansion of human cells in monolayer plays an important part. Traditionally, cell cultures have been supplemented with serum to support attachment and proliferation, but serum is a potential source of foreign protein contamination and viral protein transmission. In this study, we evaluated the use of human serum for experimental human articular chondrocyte expansion and to develop a method for preparation of large volumes of high-quality human serum from healthy blood donors. Human autologous serum contained high levels of epidermal-derived growth factor and platelet-derived growth factor-AB and supported proliferation up to 7 times higher than FCS in primary chondrocyte cultures. By letting the coagulation take place in a commercially available transfusion bag overnight, up to 250 ml of growth factor-rich human serum could be obtained from one donor. The allogenic human serum supported high proliferation rate without loosing expression of cartilage-specific genes. The expanded chondrocytes were able to redifferentiate and form cartilage matrix in comparable amounts to autologous serums. In conclusion, the transfusion bags allow preparation of large volumes of growth factor-rich human serum with the capacity to support in vitro cell expansion. The data further indicate that by controlling the coagulation process there are possibilities of optimizing the release of growth factors for other emerging cell therapies.

Characterization of Human AB Serum for Mesenchymal Stromal Cell Expansion

BACKGROUND

So far, using human blood-derived components appears to be the most efficient and safest approach available for mesenchymal stromal cell (MSC) expansion. In this paper, we report on the characterization of human AB serum (AB HS) produced by using different plasma sources, and its use as an alternative supplement to MSC expansion.

METHODS

Two plasma sources were used for AB HS production: plasma removed from whole blood after 24 h of collection (PC > 24 h) and plasma, cryoprecipitate reduced (PCryoR). The biochemical profile and quality of the produced AB HS batches were analyzed and their ability to support MSC cell growth after different storage times (0, 3, 6, 9 and 12 months) was evaluated.

RESULTS

The two plasma sources used showed similar characteristics regarding biochemical constituents and quality parameters and were effective in promoting MSC growth. MSCs cultured in medium supplemented with 10% AB HS presented similar doubling times and cumulative population doublings when compared to the 10% fetal bovine serum(FBS)-supplemented culture while maintaining immunophenotype, functional features, and cytogenetic profile.

CONCLUSION

Overall, the results indicate that AB HS is an efficient FBS substitute and can be used for at least 12 months after production without impairing cell proliferation and quality.

Culture of human cell lines by a pathogen-inactivated human platelet lysate

Alternatives to the use of fetal bovine serum (FBS) have been investigated to ensure xeno-free growth condition. In this study we evaluated the efficacy of human platelet lysate (PL) as a substitute of FBS for the in vitro culture of some human cell lines. PL was obtained by pools of pathogen inactivated human donor platelet (PLT) concentrates. Human leukemia cell lines (KG-1, K562, JURKAT, HL-60) and epithelial tumor cell lines (HeLa and MCF-7) were cultured with either FBS or PL. Changes in cell proliferation, viability, morphology, surface markers and cell cycle were evaluated for each cell line. Functional characteristics were analysed by drug sensitivity test and cytotoxicity assay. Our results demonstrated that PL can support growth and expansion of all cell lines, although the cells cultured in presence of PL experienced a less massive proliferation compared to those grown with FBS. We found a comparable percentage of viable specific marker-expressing cells in both conditions, confirming lineage fidelity in all cultures. Functionality assays showed that cells in both FBS- and PL-supported cultures maintained their normal responsiveness to adriamycin and NK cell-mediated lysis. Our findings indicate that PL is a feasible serum substitute for supporting growth and propagation of haematopoietic and epithelial cell lines with many advantages from a perspective of process standardization, ethicality and product safety.

Human adipose tissue-derived stem cells cultured in xeno-free culture condition enhance c-MYC expression increasing proliferation but bypassing spontaneous cell transformation

Introduction

Human adipose tissue-derived stem cells (hASCs) are attractive cells for therapeutic applications and are currently being evaluated in multiple clinical trials. Prior to their clinical application, hASCs must be expanded ex vivo to obtain the required number of cells for transplantation. Fetal bovine serum is the supplement most widely used for cell culture, but it has disadvantages and it is not safe for cell therapy due to the risks of pathogen transmission and immune reaction. Furthermore, the cell expansion poses a risk of accumulating genetic abnormalities that could lead to malignant cell transformation. In this study, our aim was to evaluate the proliferation pattern as well as the resistance to spontaneous transformation of hASCs during expansion in a xeno-free culture condition.

Methods

hASCs were expanded in Dulbecco’s modified Eagle’s medium supplemented with pooled allogeneic human serum or fetal bovine serum to enable a side-by-side comparison. Cell viability and differentiation capacity toward the mesenchymal lineages were assessed, along with immunophenotype. Ki-67 expression and the proliferation kinetics were investigated. The expression of the transcription factors c-FOS and c-MYC was examined with Western blot, and MYC, CDKN2A, ERBB2 and TERT gene expression was assessed with quantitative PCR. Senescence was evaluated by β-gal staining. Karyotype analysis was performed and tumorigenesis assay in vivo was also evaluated.

Results

The hASCs expanded in medium with pooled allogeneic human serum did not show remarkable differences in morphology, viability, differentiation capacity or immunophenotype. The main difference observed was a significantly higher proliferative effect on hASCs cultured in pooled allogeneic human serum. There was no significant difference in C-FOS expression; however, C-MYC protein expression was enhanced in pooled allogeneic human serum cultures compared to fetal bovine serum cultures. No difference was observed in MYC and TERT mRNA levels. Moreover, the hASCs presented normal karyotype undergoing senescence, and did not form in vivo tumors, eliminating the possibility that spontaneous immortalization of hASCs had occurred with pooled allogeneic human serum.

Conclusions

This complete characterization of hASCs cultivated in pooled allogeneic human serum, a suitable xeno-free approach, shows that pooled allogeneic human serum provides a high proliferation rate, which can be attributed for the first time to C-MYC protein expression, and showed cell stability for safe clinical applications in compliance with good manufacturing practice.

Mitogenic activity of hydroxyapatite: requirement for somatomedin C

Synovial hyperplasia is a feature of the chronic synovitis associated with basic calcium phosphate crystals [hydroxyapatite (HA), octacalcium phosphate, tricalcium phosphate] and calcium pyrophosphate. Each of these crystals stimulated mitosis of cultured human skin fibroblasts or canine synovial fibroblasts in a concentration-dependent fashion. We examined the effect of pure somatomedin C (Sm-C) on HA crystal induced mitogenesis. Confluent cultures of human fibroblasts were rendered quiescent by incubation in the presence of 1% platelet-poor-Sm-C free plasma (PPSCFP) for 24 hours. HA crystals stimulated thymidine incorporation 2.3-fold over control value. Addition of Sm-C significantly augmented the effect of HA crystals (P less than 0.01). Nearly identical effects were observed in the presence of 100 micrograms/ml HA crystals or 15 ng/ml PDGF. Monoclonal antibodies against Sm-C had little effect on the basal 3H thymidine uptake by control cells incubated in 1% PPSCFP but blocked over 50% of the HA crystal or PDGF-induced 3H thymidine incorporation both in the presence or absence of Sm-C. The incomplete blocking suggested either the presence of other "progression" factors, such as insulin-like growth factor II in the conditioned media or the possibility that HA or PDGF in high enough dosage enabled cells to escape their dependence on Sm-C for DNA synthesis.

Heparin-treated, v-myc-transformed chicken heart mesenchymal cells assume a normal morphology but are hypersensitive to epidermal growth factor (EGF) and brain fibroblast growth factor (bFGF); cells transformed by the v-Ha-ras oncogene are refractory to EGF and bFGF but are hypersensitive to insulin-like growth factors

Chicken heart mesenchymal cells do not proliferate in culture medium containing heat-defibrinogenated plasma but proliferate briskly when incubated with epidermal growth factor (EGF) or brain fibroblast growth factor (bFGF) plus insulin-like growth factors (IGFs) or when infected with sarcoma or erythroblastosis viruses. When infected with the retrovirus MC29, which bears a v-myc oncogene, chicken heart mesenchymal cells proliferate at a more modest rate and become morphologically transformed. Heparin at 25 microgram/ml causes these MC29-transformed cells to become proliferatively quiescent and to assume a normal morphology. Heparin-treated MC29-infected cells are, however, 100 times more sensitive to EGF than are their normal, uninfected counterparts. MC29-infected cells appear, likewise, to be hypersensitive to bFGF and to PDGF preparations but not to insulin. We hypothesize, therefore, (i) that heparin prevents the generation by cells of a mitogen from plasma protein precursors in the culture medium; (ii) that the v-myc oncogene renders cells hypersensitive to EGF, bFGF, PDGF, and the putative plasma-protein-derived mitogen; and (iii) that MC29-infected cells must proliferate in order to manifest the transformed morphology. Chicken heart mesenchymal cells infected with a recombinant spleen necrosis virus containing a v-ras oncogene are morphologically transformed but proliferate only sluggishly in plasma-containing medium without added mitogenic hormones. Heparin does not significantly affect their behavior. They are refractory to mitogenic stimulation by EGF or bFGF suggesting that ras proteins mediate the effects of receptors for these hormones. The SNV/v-ras-infected cells proliferate briskly, however, in response to hyperphysiological concentrations of insulin, an IGF surrogate, and are considerably more sensitive to this IGF mitogenicity than are their normal, uninfected counterparts.

Phorbol 12-myristate 13-acetate, ionomycin or ouabain, and raised extracellular magnesium induce proliferation of chicken heart mesenchymal cells

Cultured chicken heart mesenchymal cells are proliferatively quiescent at low densities in medium containing plasma at 10%. Mitogenic hormones like epidermal growth factor and insulin-like growth factors cause these cells to proliferate very actively, as does infection with avian sarcoma viruses, erythroblastosis virus, or myelocytomatosis virus. We have found that the combination of phorbol 12-myristate 13-acetate (PMA), ionomycin or ouabain, and raised extracellular magnesium, likewise, causes these cells to proliferate very actively. Although these agents have no significant effect when acting singly, the combination of PMA at 100 ng/ml and 0.5 microM ionomycin induces a 6-fold increase in cell number at 4 days, and the combination of PMA, ionomycin, and 5.6 mM magnesium induces 12-fold multiplication. Likewise, PMA plus 1 microM ouabain induces 3-fold multiplication, whereas the combination of PMA, ouabain, and magnesium induces 6-fold multiplication. The tumor promoter PMA, like diacylglycerol released by breakdown of plasma membrane phosphatidylinositol diphosphate, is known to activate the serine- and threonine-specific intracellular enzyme kinase C. The divalent cation ionophore ionomycin is known to carry calcium into cells down an electrochemical gradient, and the Na+,K+-ATPase inhibitor ouabain appears to elevate intracellular calcium by means of a sodium-mediated exchange mechanism. Magnesium, like calcium, is known to enter cells passively down an electrochemical gradient and to be involved in the regulation of many key intracellular reactions. Our findings with PMA, ionotropes, and magnesium support a hypothesis that diacylglycerol-mediated activation of kinase C plus cellular divalent cation influx and/or mobilization, caused by the action of mitogenic hormones or the protein products of onc genes, are key events in the initiation of cell replication.

Growth factor-induced proliferation of human fibroblasts in serum-free culture depends on cell density and extracellular calcium concentration

Human neonatal skin fibroblasts plated sparsely in MCDB 105 traversed a complete cell cycle in the absence of serum or serum-derived proteins. Addition of pure PDGF did not significantly increase entrance into S phase as revealed by 3H-thymidine labeling index or clonal growth on palladium islands. In subphysiologic Ca2+ concentrations or in the presence of a calmodulin inhibitor, W7, proliferation in the absence of growth factors ceased and PDGF became mitogenic. In contrast, confluent fibroblast cultures were stimulated by PDGF in physiologic Ca2+ concentrations. This was also the case with sparse adult skin fibroblast cultures while a fetal strain entered S in the absence of PDGF even in low extracellular Ca2+ concentrations. EGF gave similar results as PDGF in all experiments performed. This proposes a similar role for the two growth factors in the cell cycle. However, a difference in the mechanisms of action of PDGF and EGF is indicated by the fact that PDGF and EGF were additive at optimal concentrations when maximal growth response by a single growth factor was restricted by a subphysiologic extracellular Ca2+ concentration.

Epidermal growth factor and insulin cause normal chicken heart mesenchymal cells to proliferate like their Rous sarcoma virus-infected counterparts

Normal chicken heart mesenchymal cells at low culture density are proliferatively quiescent in a physiological culture medium containing heparinized, heat-inactivated, chicken plasma at 10%. Rous sarcoma virus-infected chicken heart mesenchymal cells, on the other hand, proliferate maximally in this same medium, undergoing a 60-fold increase in cell number during 4 days of exponential growth. When normal heart mesenchymal cells are cultured for 4 days in the presence of epidermal growth factor at 1 micrograms/ml they undergo a 16-fold increase in number, with graded responses to lower concentrations of the factor. In the presence of insulin at 10 micrograms/ml, normal heart mesenchymal cells multiply by a factor of 3 over a 4-day period. The addition of epidermal growth factor (1 microgram/ml) and insulin (10 micrograms/ml) to cultures of normal chicken heart mesenchymal cells causes these cells to proliferate at a rate comparable to that of their RSV-infected counterparts.

Calcium ions and the control of proliferation in normal and cancer cells

Several lines of evidence suggest tha Ca2+ ions control cell proliferation: Ca2+ entry into cytoplasm acts as a general mitogen; serum and serum-replacements induce Ca2+ influx; the Ca2+ concentrations in growth media required to support the proliferation of normal cells are much higher than those required for cancer cells; serum and growth factors reduce the Ca2+ requirements of normal cells; tumour promoters alter Ca2+ fluxes via a mechanism used principally by growth factors. Minor supporting evidence includes the effects of various drugs and viruses, and the behaviour of tumour cell mitochondria and intercellular junctions. It is still not possible to decide exactly where and when inside cells the critical effect of Ca2+ on proliferation occurs, but we discuss at length the practical problems of understanding Ca2+ movements in tissue-culture cells. Carried to its logical conclusion, present evidence suggests that an overridden or bypassed Ca2+ control process may be the key, common determinant of unrestrained proliferation in cancer cells.