Comparative strategic approaches to COVID-19 in Africa: Balancing public interest with civil liberties

As COVID-19 spreads rapidly across Africa, causing havoc to economies and disruption to already fragile healthcare systems, it is becoming clear that despite standardised global health strategies, national and local government responses must be tailored to their individual settings. Some African countries have adopted stringent measures such as national lockdown, quarantine or isolation, in combination with good hand hygiene, mandatory wearing of masks and physical distancing, to prevent an impending healthcare crisis. The impact of stringent measures in low- to middle-income African countries has bought time for healthcare facilities to prepare for the onslaught of COVID-19 cases, but some measures have been challenging to implement. In some settings, public health measures have been associated with serious violations of individual rights owing to abuse of power and gaps in implementation of well-intentioned policy. Collateral damage with regard to non-COVID-19 diseases that were suboptimally managed in pre-pandemic times may mean that lives lost from other diseases could exceed those saved from COVID-19. While individuals complying with lockdown regulations have embraced an acceptance of the concept of the common good, at a broad community level many are finding the transition from individualism to collective thinking required during a pandemic difficult to navigate. In this article, we look at government responses to the pandemic in six African countries (Malawi, South Africa, Uganda, Zambia, Zimbabwe and Botswana), and highlight ethical concerns arising in these contexts.

Knowledge about the research and ethics committee at Makerere University, Kampala

BACKGROUND

All research involving human participants should be reviewed by a competent and independent institutional research and ethics committee. Research conducted at Makerere University College of Health Sciences should be subjected to a rigorous review process by the ethics committee in order to protect human participants' interests, rights and welfare.

OBJECTIVE

To evaluate researchers' knowledge about the functions and ethical review process of the College of Health Sciences research and ethics committee.

METHODS

A cross sectional study. 135 researchers consented to participate in the study, but 70 questionnaires were answered giving a 52% response.

RESULTS

Age ranged between 30 to 61 years, majority of participants 30-39 years. Most of the respondents do agree that the REC functions include Protocol review 86%, protection of research participants 84.3%, and monitoring of ongoing research. During ethical review, the RECpays special attention to scientific design [79.7%] and ethical issues [75.3%], but less to the budget and literature review. More than 97% of the respondents believe that the REC is either average or very good, while 2.8% rank it below average.

CONCLUSION

Respondents knew the major functions of the committee including protection of the rights and welfare of research participants, protocol review and monitoring of on going research, and the elements of protocol review that are given more attention include ;scientific design and ethical issues. Overall performance of the REC was ranked as average by respondents. The committee should limit delays in approval and effectively handle all functions of the committee.

Induction of tumorigenicity by galectin-3 in a nontumorigenic human breast-carcinoma cell-line

The human galectin-3 is a galactoside-binding protein of 31 kDa which functions as a receptor for glycoproteins containing poly N-acetyllactosamine side chains and as a substrate for matrix metalloproteinases-2 and -9. We studied its expression by flow cytoflourimetry, Western, Northern and Southern analyses, in five cultured human breast carcinoma cell lines previously characterized as nontumorigenic, poorly metastatic or metastatic in nude mice. The expression of galectin-3 correlated with the reported tumorigenicity of the cells. The introduction of recombinant galectin-3 into the null expressing non-tumorigenic BT-549 cells resulted in the acquisition of anchorage-independent growth properties in all and tumorigenicity in 3/4 sense transfected cell clones. The data indicate a relationship between galectin-3 expression and malignancy of human breast carcinoma cell lines.

Galectin-3 mediates the endocytosis of beta-1 integrins by breast carcinoma cells

Galectin-3, a beta-galactoside binding lectin, has been demonstrated to play a key role(s) in cell to extracellular matrix interaction. The precise mechanism by which it modulates cellular adhesion is presently unclear and warrants further studies. We hereby report that galectin-3 mediates the endocytosis of beta-1 integrins in a lactose-dependent manner. Interestingly we observed that galectin-3 was also rapidly internalized by the cells via the same pathway and the internalization was completely blocked by lactose. The endocytosis process was temperature dependent and was inhibited by filipin but not chlorpromazine. The endocytosis of galectin-3 and beta-1 integrins by the cells was accompanied by rapid cell spreading due to cytoskeletal reorganization. The data suggest a novel mechanism by which galectin-3 and beta-1 integrins are internalized into breast carcinoma cells via a cavaleolae-like pathway of endocytosis.

Rapid release of intracellular galectin-3 from breast carcinoma cells by fetuin

Galectin-3, a beta-galactoside binding protein, plays a significant role in cell to extracellular matrix interactions. Despite its extracellular expression, the precise physiological mechanisms that trigger its release from the intracellular milieu have not been characterized. The present analyses were, therefore, done to identify the extracellular matrix proteins with propensity to induce the release of intracellular galectin-3 from breast carcinoma cells. Our studies demonstrate that fetuin, a serum glycoprotein that is abundant in the fetal serum, is capable of inducing the rapid release (approximately 1 min) of intracellular galectin-3 from the cells. The mechanism by which galectin-3 is rapidly released appears to be novel and does not depend on changes in intracellular calcium levels. We also report that galectin-3-expressing breast carcinoma cells in serumless medium adhere and spread well on microtiter wells in the presence of fetuin and divalent ions in a carbohydrate-dependent manner. The data suggest that fetuin is a natural modulator of galectin-3 secretion/release and that the secreted galectin-3 modulates the activity of cell surface receptors for extracellular matrix proteins.

Geographic distribution and frequency of a taurine Bos taurus and an indicine Bos indicus Y specific allele amongst sub-saharan African cattle breeds

We report for the first time, and for the whole of sub-Saharan Africa, the geographical distribution and the frequency of an indicine and a taurine Y specific allele amongst African cattle breeds. A total of 984 males from 69 indigenous African populations from 22 countries were analysed at the microsatellite locus INRA 124. The taurine allele is probably the oldest one on the continent. However, the taurine and the indicine alleles were present in 291 males (30%), and 693 males (70%), respectively. More particularly, 96% of zebu males (n = 470), 50% of taurine males (n = 263), 29% of sanga males (crossbreed Bos taurus x Bos indicus, n = 263) and 95% of zebu x sanga crossbred males (n = 56) had the indicine allele. The Borgou, a breed classified as zebu x taurine cross showed only the zebu allele (n = 12). The indicine allele dominates today in the Abyssinian region, a large part of the Lake Victoria region and the sahelian belt of West Africa. All the sanga males (n = 64) but only one from the Abyssinian region had the indicine allele. The taurine allele is the commonest only among the sanga breeds of the southern African region and the trypanotolerant taurine breeds of West Africa. In West Africa and in the southern Africa regions, zones of introgression were detected with breeds showing both Y chromosome alleles. Our data also reveal a pattern of male zebu introgression in Mozambique and Zimbabwe, probably originating from the Mozambique coast. The sanga cattle from the Lake Victoria region and the Kuri cattle of Lake Chad, cattle populations surrounded by zebu breeds were, surprisingly, completely devoid of the indicine allele. Human migration, phenotypic preferences by the pastoralists, adaptation to specific habitats and to specific diseases are the main factors explaining the present-day distribution of the alleles in sub-Saharan Africa.

Novel mechanism that Trypanosoma cruzi uses to adhere to the extracellular matrix mediated by human galectin-3

Binding of Trypanosoma cruzi trypomastigotes to laminin is enhanced by galectin-3, a beta-galactoside binding lectin. The galectin-3 enhanced binding of trypanosomes to laminin is inhibited by lactose. Co-immunoprecipitations indicate that galectin-3 binds to the 45, 32 and 30 kDa trypanosome surface proteins. Binding of galectin-3 to the 45, 32 and 30 kDa surface proteins is inhibited by lactose. Polyclonal and a monoclonal antibodies to galectin-3 immunoprecipitated a major 64 kDa trypanosome surface protein. T. cruzi monoclonal antibody to mucin recognized the 45 kDa surface protein. The 45, 32 and 30 kDa surface proteins interact with galectin-3 in order to enhance trypanosome adhesion to laminin.

Galectin-3 regulates the adhesive interaction between breast carcinoma cells and elastin

Galectin-3 is a beta-galactoside binding lectin whose precise physiological role is not yet defined. In the present studies, we questioned whether galectin-3 plays a role in the adhesion of breast carcinoma cells to elastin. The impetus for this analysis was the initial observation that the cellular receptor for elastin, the 67 kDa elastin/laminin protein may have galectin-like properties (Mecham et al. [1989] J. Biol. Chem. 264:16652-16657). We therefore analyzed the adhesion of breast carcinoma cells to microtiter wells coated with elastin under conditions which eliminate integrin participation in adhesion. The adhesion assay was done in the absence and presence of purified recombinant galectin-3. We hereby demonstrate that high concentrations of galectin-3 ligate breast carcinoma cells to microtiter wells coated with elastin. Galectin-3 also demonstrated a specific binding interaction with purified elastin in a dose and lactose dependent manner. Furthermore we demonstrated by immunoprecipitation that endogenous galectin-3 in breast carcinoma cells is associated with tropoelastin. Lastly, the breast carcinoma cells which expressed galectin-3 on their surface, demonstrated enhanced cellular proliferation on elastin compared to galectin-3 null expressing cells. These studies suggest that galectin-3 is capable of regulating the interactions between cells and elastin.

Galectin-3 regulates the adhesive interaction between breast carcinoma cells and elastin

Galectin-3 is a beta-galactoside binding lectin whose precise physiological role is not yet defined. In the present studies, we questioned whether galectin-3 plays a role in the adhesion of breast carcinoma cells to elastin. The impetus for this analysis was the initial observation that the cellular receptor for elastin, the 67 kDa elastin/laminin protein may have galectin-like properties (Mecham et al. [1989] J. Biol. Chem. 264:16652-16657). We therefore analyzed the adhesion of breast carcinoma cells to microtiter wells coated with elastin under conditions which eliminate integrin participation in adhesion. The adhesion assay was done in the absence and presence of purified recombinant galectin-3. We hereby demonstrate that high concentrations of galectin-3 ligate breast carcinoma cells to microtiter wells coated with elastin. Galectin-3 also demonstrated a specific binding interaction with purified elastin in a dose and lactose dependent manner. Furthermore we demonstrated by immunoprecipitation that endogenous galectin-3 in breast carcinoma cells is associated with tropoelastin. Lastly, the breast carcinoma cells which expressed galectin-3 on their surface, demonstrated enhanced cellular proliferation on elastin compared to galectin-3 null expressing cells. These studies suggest that galectin-3 is capable of regulating the interactions between cells and elastin.

Regulation of cellular adhesion to extracellular matrix proteins by galectin-3

The control of cellular adhesion to extracellular matrix proteins is poorly understood. In the present analyses, we set out to test the hypothesis that high galectin-3 concentration on the cell surface downregulates cellular adhesion to the extracellular matrix proteins. Various tumor cell lines were briefly incubated without or with galectin-3 and then allowed to adhere to wells coated with laminin-1, collagen IV and fibronectin. Our data demonstrated that the cells which were incubated with galectin-3 prior to plating had significantly reduced adhesion to extracellular matrix proteins. This inhibition involved the carbohydrate recognition domain of the lectin because adhesion was achieved in the presence of galectin-3 and lactose but not galectin-3 and sucrose. Furthermore we demonstrated that galectin-3 associates with alpha 1 beta 1 integrin in a lactose dependent manner.

Adhesion of human breast carcinoma to extracellular matrix proteins is modulated by galectin-3

In this report, we have analyzed the adhesive interactions of a breast carcinoma cell line, BT-549, and its galectin-3-transfected subclone 11-9-1-4 with laminin, collagen IV and fibronectin. We determined that 11-9-1-4 cells adhered much more rapidly (within 1 h of plating) to laminin- and collagen IV-coated wells than the galectin-3 null expressing BT-549 cells. However, after 24 h, both cell lines fully adhered to laminin and collagen IV. Both cell lines also achieved maximum adhesion to fibronectin within 30 min. Not only did 11-9-1-4 express galectin-3 in the usual punctate pattern on its cell surface, it demonstrated a higher surface expression of alpha 6 beta 1 integrin compared to BT-549. The 11-9-1-4 cells were able to invade through matrigel-coated polycarbonate filters at approximately 3 times the rate of BT-549 parental cells. Our data suggest that galectin-3 is essential for adhesion to laminin and collagen IV but not fibronectin by breast carcinoma cells. In addition, galectin-3 expression may modulate the surface expression of some of the integrins specific for laminin and collagen IV adhesion and invasion of basement membrane by breast carcinoma cells.

Modulation of the biological functions of galectin-3 by matrix metalloproteinases

Galectin-3 is an important intracellular and extracellular lectin which is presumed to interact with extracellular matrix proteins and cell surface glycoproteins in normal and pathophysiological conditions. The exact physiological role of the protein is presently not known. We have previously demonstrated that recombinant human galectin-3 is a novel substrate for metalloproteinases, particularly MMP-2 and MMP-9. These enzymes are capable of efficiently cleaving the Ala62-Tyr63 bond of the ca. 30 kDa galectin-3, generating a 22 kDa fragment with intact carbohydrate recognition domain and a ca. 9 kDa polypeptide comprising the amino terminal end of the intact galectin-3. In this study, we analyzed interactions of the 22 kDa fragment of galectin-3 with immobilized laminins. We have also compared the hemagglutination as well as homodimerization potentials of this fragment with that of intact galectin-3. Our data suggest that cleavage of galectin-3 by metalloproteinases; (a) alters the carbohydrate recognition domain of the lectin so that it binds more tightly to the glycoconjugates and, (b) reduces selfassociation of the galectin molecules thereby abrogating the biological properties dependent on such associations or homodimerization.

Establishment of breast cell cultures and lines from peoples of African origin

OBJECTIVES

The purpose of our study was to establish breast epithelial cell cultures and cell lines from peoples of African origin (blacks). It is presumed that the biology of breast cancer in women of African origin has unique aspects that can be explored using cultured breast epithelial cells.

STUDY DESIGN

Biopsy specimens were obtained from black women undergoing radical or modified mastectomies. Normal cell cultures were established using tissue from reduction mammaplasties or the milk of lactating mothers. The tissue specimens were lacerated, digested with collagenase solution, and plated on tissue culture plates. To extend the life of the epithelial cells in culture, they are transformed with SV40 virus.

RESULTS

We have maintained breast tumor cells in culture from a 27-year-old black woman for more than 1 month.

CONCLUSION

Despite the difficulty of establishing epithelial cell cultures, we have maintained breast tumor cells from blacks in culture for an extended period to allow characterization.

The interactions of alpha 2HS glycoprotein with metalloproteinases

The objective of the present analyses was to determine whether matrix metalloproteinases interact with alpha 2HS glycoprotein, the human homologue of bovine fetuin. Alpha 2HS glycoprotein was incubated with metalloproteinases at 1:1 and 1:10 molar ratios. The serum glycoprotein was completely degraded by gelatinase-A and matrilysin at the higher enzyme concentration after an overnight incubation at 37 degrees C. The data show that gelatinase-A, matrilysin and gelatinase-B do interact with alpha 2HS glycoprotein and that gelatinase-B associates most tightly with the serum glycoprotein.

Phenylacetic acid halides inhibit estrogen receptor (ER)-positive MCF-7 cells, but not ER-negative human breast cancer cells or normal breast epithelial cells

Phenylacetic acid (PA) derivatives and conjugates have been reported to have antiproliferative and antitumor properties against various types of cancers. Based on these findings, recent in vitro experiments were devised to examine the antiproliferative properties of a series of para substituted (Br, Cl, F, H, NO2 and OCH3) PAs. The in vitro screening protocal involved the plating of MCF-7 cells in a 96-well plate assay. After 1 day, the cells were exposed to the PA derivatives for 2 days (log phase of MCF-7 growth curve). Cells growth was determined by the Alamar blue dye reagent. The optical density data was analyzed and IC50 concentration values determined. The results showed that PA halide derivatives caused a significant decrease in proliferation of the MCF-7 cells. The order of antiproliferative activity was BR > Cl > or = F, with IC50 values (nM) of 10 +/- 0.005, 100 +/- 0.02 and 100 +/- 0.04, respectively. The OCH3, H and NO2 compounds showed no significant antiproliferative activity. PA halide derivatives may have similar actions as tamoxifen because they show specificity for estrogen receptor-positive cells.

Galectin-3 binding potentials of mouse tumor EHS and human placental laminins

Galectin-3, a lectin which binds to polyalctosamine chains of laminin, has been implicated as a modulator of cell to laminin interactions. In this study, we analyzed the relative binding of galectin-3 to mouse tumor and human placental laminins. Using gel overlay experiments, we have demonstrated that galectin-3 preferentially binds to mouse tumor compared to human placental laminin. We have also demonstrated by Western blotting assays that mouse tumor laminin copurifies with endogenous mouse galectin-3. Lastly, we have demonstrated by periodate Schiff staining that mouse tumor has more sugar residues than human placental laminin. These analyses may explain why laminins purified from normal and tumor cells promote the attachment and spreading of certain cells differently.

Interactions of gelatinases with soluble and immobilized fetuin and asialofetuin

We have analyzed the interactions of human and mouse gelatinases with fetuin and asialofetuin. The data showed that recombinant human gelatinase A (MMP-2) and B (MMP-9) were both specifically bound to asialofetuin and fetuin immobilized to activated agarose (affigel) with subsequent cleavage of the enzymes to lower molecular weight forms, which were likewise bound to asialofetuin/fetuin. The binding of gelatinases to immobilized forms of asialofetuin and fetuins was abrogated in the presence of either soluble fetuin or asialofetuin. Endogenous mouse macrophage gelatinases (mol wt 92 and approximately 52 kDa) were also specifically bound to immobilized asialofetuin upon which the two forms of the gelatinases were reduced to a approximately 45-kDa fragment. The binding of the approximately 45-kDa fragment to asialofetuin was also abrogated in the presence of either soluble fetuin or asialofetuin. Whereas only the activated MMP-2 bound to immobilized asialofetuin had significant gelatinolytic activity, both the zymogen and the activated forms of MMP-9 hydrolyzed soluble [3H]gelatin to the same extent while still bound to asialofetuin. Our data suggest that cell surface bound fetuin/asialofetuin could perform two functions: they could (a) act as cell surface receptors or anchors for MMP-2 and MMP-9 and (b) bind and activate MMP-9 on the cell surface.

The growth inhibitory properties of a dopamine agonist (SKF 38393) on MCF-7 cells

Dopamine agonists have been indicated as treatment for disorders such as Parkinson's disease, cardiogenic shock and dopamine insufficiency. A unique relationship exists between dopamine and carcinogenicity. Chronic prolactin stimulation has been identified as a promoter of carcinogenicity. Prolactin secretion is regulated through dopamine receptor activation. Dopaminergic agonists inhibit prolactin release and antagonists increase release. High levels of prolactin have been shown to suppress production of estrogen and progesterone. As a result of these findings, a series of experiments were designed to examine the effects of a specific dopamine agonist, SKF 38393, against MCF-7 cells. MDA-MB231 and MCF-10 cells were used as negative controls. The breast cancer in vitro screening procedure involved the plating of MCF-7, MDA-MB231 and MCF-10 cells in a 96-well plate assay. After 1 day, the cells were exposed to SKF 38393 for 2 days and cell growth was determined by the Alamar blue dye reagent method. The optical density data was analyzed and IC50 values determined. The results indicated that SKF 38393 caused a significant decrease in proliferation of MCF-7 cells. The IC50 value was 0.1 +/- 0.03 microM. The results also indicated no significant effect on MDA-MB231 and MCF-10 cells.

Galectin-3 is a novel substrate for human matrix metalloproteinases-2 and -9

The primary structure of galectin-3, a approximately 30 kDa galactoside-binding protein (aka CBP-35, mL-34, hL-31, L-29, Mac-2, and epsilon BP), reveals two structural domains: an amino-terminal domain consists of a Pro-Gly-rich motif, and a globular carboxyl-terminal domain containing a carbohydrate-binding site. In this study, we report that the amino-terminal domain of galectin-3 contains a cleavage site for two members of the matrix metalloproteinase family of enzymes: the 72 kDa (gelatinase A, MMP-2) and the 92 kDa (gelatinase B, MMP-9) proteinases. The major cleavage site for the gelatinases in galectin-3 is at the Ala62-Tyr63 bond, and its hydrolysis by these enzymes was inhibited by TIMP-2. Cell-surface expression of galectin-3 was reduced following treatment of viable T47D human breast carcinoma cells with gelatinase A. These results suggest that galectin-3 may be a substrate for gelatinases and that its degradation may play a role in modulating the biological activities of galectin-3.

The effect of leprosy management on leprosy complications at Alupe Hospital, Busia, Kenya

A retrospective study of leprosy complications among new cases recruited for multiple drug therapy (MDT) at Alupe Leprosy Hospital between January 1986 and January 1992 was carried out to determine their prevalence, incidence and their relationship with disease classification. Out of 154 cases studied majority fell in the Borderline tuberculoid (BT) class (47%). The total follow up period was 186 person years giving an overall incidence rate of reactions of 20 per 100 person years. Overall point prevalence of complications for both males and females were highest in the extremities and ranged between 10% and 46% while the overall period prevalence ranged between 14% and 73% per year. There was a significant number of incident cases of complications during the follow-up period and comparison of different complications with different disease classes had odds ratios of around unity showing that MDT alone as an intervention measure plays no significant role in onset or progress of leprosy complications. It is observed that Borderline tuberculoid (BT) and Borderline lepromatous (BL) leprosy patients are at the highest risk of developing leprosy complications.

Regulation of the expression of galactoside-binding lectin during human monocytic differentiation

The widely distributed hL-31 (CBP35, epsilon BP, mL-34, L-29, Mac-2) is a Ca(2+)-independent galactoside-binding lectin which functions as a receptor on mammalian cells for glycoproteins containing poly-N-acetyllactosamine side chains. Little is known about the regulation of its expression. The human promyelocytic leukemia cell line, HL-60, was used to determine whether expression of hL-31 (Mac-2) correlated with macrophage/monocyte differentiation. Nondifferentiated HL-60 cells and HL-60 cells grown in the presence of 1.24 microM retinoic acid expressed only trace amounts of hL-31. In contrast, both hL-31 transcripts and protein were detected at 8 h after addition of 17 nM 12-O-tetradecanoylphorbol-13-acetate and reached maximal levels at 24 h. Addition of actinomycin D along with 12-O-tetradecanoylphorbol-13-acetate blocked accumulation of hL-31 mRNA. In contrast, addition of actinomycin D to 12-O-tetradecanoylphorbol-13-acetate-treated HL-60 cells that had already accumulated high levels of hL-31 mRNA did not cause significant reduction in RNA levels until 6-8 h had elapsed. Since increased hL-31 expression was not associated with an increase in transcriptional activity of the hL-31 gene, these results suggest that hL-31 expression is regulated at the posttranscriptional level, at least in part, by stabilization of its mRNA. The results also indicate that the processes leading to increased hL-31 expression in HL-60 cells may be specific to differentiation along the monocyte/macrophage pathway.

Structure-function relationship of a recombinant human galactoside-binding protein

A galactoside-binding lectin (hL-31) containing a collagen-like sequence was identified in human tumor cells. It was found to be the homologue of the IgE-binding protein, the macrophage cell-surface Mac-2 antigen, and the murine CBP35, RL-29, and mL-34 lectins. Here we report on the expression in Escherichia coli and functional analysis of recombinant hL-31 (rhL-31). The rhL-31 was purified in one step through an asialofetuin affinity column. The rhL-31 was reactive to anti-lectin antibodies and retained its lactose-dependent hemagglutination of trypsin-treated glutaraldehyde-fixed rabbit erythrocytes. The rhL-31 elutes from an affinity column as a 31-kDa monomer and undergoes homodimerization at relatively high protein concentrations, comparable to those used to mediate hemagglutination. Electron microscopy showed that the rhL-31 appears as a Y-shaped structure. Lactoperoxidase-catalyzed iodination of murine tumor cell-surface proteins followed by collagenase treatment revealed that the lectin is probably a peripheral membrane protein whereby both the amino and the carboxy termini are exposed on the outer cell membrane. These results point to the membrane disposition and orientation of the lectin and suggest a mechanism for a structure-function relationship of lectin activity.

Dichotomy in the laminin-binding properties of soluble and membrane-bound human galactoside-binding protein

Recent studies indicate that galactoside-binding proteins may bind the poly-N-acetyllactosamine sequences of laminin. We questioned whether human galactoside-binding protein (hL-31) binds to laminin and whether cells that express hL-31 on their surface use it as a laminin receptor to promote cellular attachment. The data show that both lectin and cells bind to immobilized laminin. The binding of soluble lectin to laminin is inhibited by lactose, while cell adhesion to it is not. The results indicate that laminin may be a ligand for soluble galactoside-binding proteins.

Buffering of intracellular calcium in response to increased extracellular levels in mortal, immortal, and transformed human breast epithelial cells

Extracellular levels of calcium at 1.05 mM or higher induce terminal differentiation and senescence in the mortal (MCF-10M) line of human breast epithelial cells, but does not retard the growth or induce differentiation in the immortal (MCF-10A) and oncogene transformed (MCF-10AneoT) lines. Intracellular levels of calcium and inositol triphosphate were determined in MCF-10M, MCF-10A, and MCF-10AneoT, under conditions of low and high extracellular calcium. We hereby report that increases in extracellular calcium is translated into significant increases in intracellular levels of calcium and inositol triphosphate in MCF-10M, but not in MCF-10A and MCF-10AneoT. This difference in the apparent calcium buffering capacity between the mortal and the immortalized human breast epithelial cells could account for the latter's unperturbed growth potential in high extracellular calcium environment.

Calcium-mediated modulation of microtubule assembly in human breast epithelial cells

Normal human breast epithelial cells obtained from a reduction mammoplasty (S130) have been maintained in culture for up to a year in Ham's F12:Dulbecco's medium, with 5% equine serum and a low calcium concentration (0.04 mM). These cells undergo senescence and terminal differentiation if they are switched to high Ca2+ medium (1.05 mM). To clarify the mechanism by which Ca2+ regulates the growth of these cells, we studied the role of tubulin assembly-disassembly and the morphologic changes subsequent to high Ca2+ switch. An early Passage (9) of S130 breast epithelial cells growing in low Ca2+ medium was analyzed. Of a total of 785 counted cells, 720 (92%) were rounded and 65 (8%) were flat, elongated, and fibroblastlike. When the cells were switched to high Ca2+ medium, out of 553 cells, only 111 (20%) were rounded and the remaining 442 (80%) were elongated and fibroblastlike. Immunocytochemical localization of tubulin, using the immunogold silver enhancement technique, showed that the majority of low Ca2(+)-grown cells did not display a network of tubulin fibers, whereas high Ca2(+)-grown cells revealed extensive cytoplasmic network of polymerized tubulin, which seemed to stretch out the cells. Experiments designed to determine the mechanisms of tubulin polymerization in these cells revealed that: a) Cells grown in high Ca2+ medium containing 0.1 mM colchicine had a reduced proportion of elongated cells; b) treatment of the cells with the calcium ionophore A23187 in low calcium medium resulted in an increase in the number of elongated cells which had more polymerized tubulin; and d) treatment of the cells with cyclic-AMP in low Ca2+ medium had no observable effect on cell morphology. These results indicate that high levels of Ca2+ either favor tubulin polymerization or stabilize the polymerized state.

Altered queuine modification of transfer RNA involved in the in vitro transformation of Chinese hamster embryo cells

Altered queuine modification of tRNA has been correlated to neoplastic transformation, but no direct cause and effect relationship has been defined. In the present study, a potential role for this alteration has been assigned. The tRNA in normal Chinese hamster embryo cells is significantly more queuine modified than the tRNA in their transformed Chinese hamster embryo counterparts, even though the specific activity of the queuine modification enzyme is much lower in Chinese hamster embryo cells than in transformed Chinese hamster embryo cells. Substrate availability appears to be responsible for the queuine hypomodification of tRNA in the transformed cells, since addition of excess exogenous queuine to the culture medium results in incorporation of queuine into the anti-codon of the undermodified tRNAs. Most importantly, the excess queuine inhibits anchorage-independent growth of transformed Chinese hamster embryo cells, thereby implicating queuine hypomodification of tRNA in the expression of this transformed phenotype.

Inhibition of phorbol ester-mediated phenotypic changes in cultured cells by hypoxanthine

Hypoxanthine induces the differentiation of certain transformed cells in vitro, so analyses were undertaken to determine whether this purine metabolite might influence the expression of transformed phenotypes induced in normal cells by chemical agents. Chinese hamster embryo cells and human skin fibroblasts in culture were treated with the promoting agent phorbol-12,13-didecanoate (PDD) with or without prior treatment with 3-methylcholanthrene (MCA), and various phenotypic effects were monitored. Hypoxanthine was found to inhibit significantly the formation of type III foci and the increase in saturation density observed for Chinese hamster cells treated with MCA plus the phorbol ester. Inosine and the hypoxanthine analogue allopurinol could also mediate the effect on saturation density, while xanthosine could not. An increase in the saturation density of human skin fibroblasts, which can be induced by the phorbol ester alone, was also inhibited by hypoxanthine. There was no significant effect on the growth rate or the intracellular nucleotide pools with hypoxanthine-treated cells. The results suggest that a normal purine metabolite, hypoxanthine, can modulate the expression of transformed phenotypes induced in vitro by the known tumor promotor PDD. These observations could help in elucidating the cellular basis for promotion of carcinogenesis.