Prolactin induced reversal of glucocorticoid mediated apoptosis of immature cortical thymocytes is abrogated by induction of tumor
Introduction
During tumorigenesis several T cell functions are greatly impaired in peripheral organs of tumor-bearing hosts (Handel-Fernandez et al., 1997, Levey and Srivastava, 1996). Thymus, the major site for T cell maturation, is severely affected by tumor development (Anderson et al., 1996, Adkins et al., 2000, Shanker et al., 2000), with a drastic decrease in CD4+ CD8+ thymocyte population in tumor-bearing animals (Fu et al., 1989). However, the mechanism involved in this phenomenon remains to be elucidated. The CD4+ CD8+ cells are known to be especially sensitive to apoptotic signals and represent the major cell type that undergoes apoptosis during the normal course of thymus development (Gruber et al., 1994). An increase in apoptosis of CD4+ CD8+ thymocytes and arrest in differentiation of the CD4− CD8− thymocytes was observed in tumor-bearing animals (Adkins et al., 2000). The CD4+ CD8+ thymocytes organize and modulate thymic functions by secreting factors for maturation of other cells of T cell lineages. These factors play an important role in gene expression programme of the next generation of T cell progenitors (Silva-Santos et al., 2005). It is likely that any alteration in CD4+ CD8+ thymocytes could lead to impaired T cell-mediated immune responses.
Neuroendocrines regulate the development of thymocytes within the thymus where glucocorticoid hormone (GC) plays a pivotal role (Savino and Dardenne, 2000). The GC sensitivity of thymocytes varies during their differentiation in thymus, being highest in CD4+ CD8+ double positive thymocytes, the critical stage at which T cell selection takes place (Ashwell et al., 2000). The hormone plays a dual role in determining the spectrum of emerging thymocytes, being involved in both, “death by neglect” and setting the threshold for TCR-induced positive selection (Ashwell et al., 2000). Production of corticosteroids in response to stress stimulus can result in complete ablation of the thymus (Tarcic et al., 1998). The exposure of mice to restrained stress leads to rise in endogenous GC level, involution of thymus and decrease of CD4+ CD8+ thymocyte subsets (Gruber et al., 1994, Tarcic et al., 1998) suggesting that GC is involved in stress induced thymic involution (Sapolsky et al., 2000, Ayala et al., 1995). It may be argued that, since malignancy is a stressful condition, increase in circulating GC level in tumor-bearing animals may be involved in thymic atrophy. However, adrenalectomy of mice followed by tumor implantation did not result in reversal of thymic atrophy. The serum GC level of tumor-bearing animals was similar to that of normal mice (Fu et al., 1989). Notably thymic atrophy associated with loss of CD4+ CD8+ thymocytes was also observed during ageing (Miller, 1996). Growth hormone (GH) and prolactin (PRL) were shown to reverse the involution of thymus in aged animals. In hyperprolactinemic Snell Bagg mouse (Foster et al., 2000) and aged rats (Nagy et al., 1983, Li et al., 1992), abnormal accumulation of CD4+ CD8+ cells was detected in lymph node. In these animals the dramatic loss of double positive thymocytes and the abnormal presence of these immature cells in the periphery was reversed by administration of PRL or GH (Kelley et al., 1986, Dorshkind and Horseman, 2000). Expression of the prolactin receptor (PRL-R) on thymocytes (Kooijman and Gerlo, 2002) and thymic dendritic cells (Carreno et al., 2004), coupled with our observations that PRL regulates thymocyte proliferation and cytokine secretion in vitro (Biswas and Chattopadhyay, 1992, Chattopadhyay and Biswas, 2002) suggest that PRL plays an important role in regulation of thymocyte differentiation. However, thymocyte differentiation in PRL−/− or PRL-R−/− mice was found to be normal (Horseman et al., 1997, Bouchard et al., 1999) indicating that PRL/PRL-R mediated interaction was not a critical requirement for thymus development.
Stress caused by burn induced acute myelopoiesis in PRL−/− mice. PRL restored the suppressed function of macrophages and splenocytes during trauma, hemorrhage and infection shock (Dugan et al., 2002, Murphy et al., 1993, Zellweger et al., 1996) and altered the sensitivity of the thymocytes during stress (Gala, 1990). PRL could reverse the GC-induced apoptosis of rat lymphoma cell line (Nb2) (Krumenacker et al., 1998). The hormone could also reverse the GC mediated suppression of thymocyte proliferation and interleukin (IL)-1 secretion (Biswas and Chattopadhyay, 1992, Chattopadhyay and Biswas, 2002) and administration of PRL blocked the apoptosis of CD4+ CD8+ thymocytes of GC-treated PRL−/− mice (Krishnan et al., 2003).
Immature cortical CD4+ CD8+ thymocytes express glycan chain that is recognized by galactose specific peanut agglutinin (PNA) (Holladay et al., 1993). In this paper, we describe the sensitivity of the PNA+ thymocytes of Elrich's ascitic carcinoma (EAC)-bearing mice to the stress stimulus GC. In this connection, we compared the efficacy of PRL in regulation of Dex-induced apoptosis of the immature cortical thymocytes of normal and tumor-bearing mice. The PRL-induced expression of the anti-apoptotic protein, Bcl-2 (Sentman et al., 1991) and regulation of PRL-R of the immature cortical thymocyte during malignancy was monitored. Since thymic atrophy was observed in normal mice injected with tumor-associated factors (Lopez et al., 1991), the involvement of tumor-derived factors in modulation of PRL-mediated reversal of GC-induced thymocyte apoptosis was also assessed.
Section snippets
Animals
Female 6-week-old Swiss mice, bred and maintained in the Animal Care and Maintenance Facility of Chittaranjan National Cancer Institute, Kolkata, were used in the study. The experiments with animals were conducted in accordance with the Animal Ethical Committee guidelines of the Institute.
Tumor
A transplantable EAC-bearing mice was used as tumor model. EAC was grown in a group of 6-week-old female Swiss mice by weekly intraperitoneal inoculation as described elsewhere (Biswas and Chattopadhyay, 1992).
Dex induces death of immature cortical thymocytes of normal and tumor-bearing mice
Analysis of relative fluorescence intensity showed that thymocytes of 3-day EAC-bearing mice, stained with both FITC-conjugated anti-mouse CD4 and PE-conjugated anti-mouse CD8 MAbs, had marginally lower number of CD4+ CD8+ cells (78.4%) compared to that of normal mice (84.8%) in total thymocyte population (Fig. 1A). Flow cytometric analysis of the PNA+ thymocytes of normal and tumor-bearing mice revealed 90% of the cells to be CD4+ CD8+ (Fig. 1B) indicating that the major subpopulation of PNA+
Discussion
Thymocyte differentiation is critical for homeostasis and normal functioning of the immune system and its dysregulation may lead to the increase in autoreactive cells or reduced survival of lymphoid cells resulting in profound immune deficiency (Benoit and Mathis, 1999, Bouillet et al., 1999). GC and PRL are important mediators of neuroendocrine regulation of thymocyte differentiation and maintenance of neuroendocrine-immune homeostatic axis (Savino and Dardenne, 2000, Berczi and Nagy, 1987).
Acknowledgements
Women Scientists Scheme SR/WOS-A/LS-121/2003 of the Department of Science and Technology, Government of India, New Delhi-110 016 awarded to R.B. supported part of the work. The authors are grateful to their colleague Rathin Baral for his help with flow cytometry.
References (72)
- et al.
A prolactin dependent immune cell line (Nb2) express a mutant form of prolactin receptor
J. Biol. Chem.
(1991) A rapid sensitive method for quantitation of microgram quantities of protein using the principle of protein dye binding
Anal. Biochem.
(1976)- et al.
Prolactin stimulates maturation and function of rat thymic dendritic cells
J. Neuroimmunol.
(2004) - et al.
Prolactin regulates macrophage and NK cell mediated inflammation and cytotoxic response against tumor
- et al.
The host–tumor immune conflict: from immunosuppression to resistance and destruction
Immunol. Today
(1997) - et al.
Humoral and cell mediated immunity in mice with genetic deficiencies of prolactin, growth hormone, insulin-like growth factor-1, and thyroid hormone
Clin. Immunol.
(2000) The physiology and mechanism of stress induced changes in prolactin secretion in the rat
Life Sci.
(1990)- et al.
Prolactin expression in immune system
- et al.
Alterations in T cells of cancer bearers: whence specificity?
Immunol. Today
(1996) - et al.
Effect of prolactin on natural killer and MHC-restricted cytotoxic cells
Interleukin-2 induces apoptosis in mouse thymocytes
Cell. Immunol.
VEGF inhibits T cell development and may contribute to tumor immune suppression
Blood
Measurement of growth and viability of cells in culture
Methods Enzymol.
Bcl-2 inhibits multiple forms of apoptosis but negative selection in thymocytes
Cell
Restraint stress-induced thymic involution and cell apoptosis are dependent on endogenous glucocorticoids
J. Neuroimmunol.
Prolactin blocks glucocorticoid induced cell death by inhibiting the disruption of mitochondrial membrane
Leuk. Res.
Signal transduction by prolactin receptors
Early block in maturation is associated with thymic involution in mammary tumor-bearing mice
J. Immunol.
Cellular interactions in thymocyte development
Annu. Rev. Immunol.
Glucocorticoids in T cell development and functions
Annu. Rev. Immunol.
The induction of accelerated thymic programmed cell death during polymicrobial sepsis: control by corticosteroids but not tumor necrosis factor
Shock
Differential expression of interferon regulatory factor-1 (IRF-1), IRF-2 and interferon consensus sequence binding protein genes in lipopolysaccharide (LPS) responsive and LPS hyporesponsive macrophages
Infect. Immun.
The effect of prolactin and growth hormone on hemolymphopoietic tissue and immune function
T lymphocyte differentiation and biology
Tamoxifen inhibition of prolactin action in the mouse mammary gland
Endocrinology
Antiestrogen inhibition of prolactin-induced growth of the Nb2 rat lymphoma cell line
Cancer Res.
Altered prolactin response of lymphocytes of tumor bearing mice
Int. J. Cancer
Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice
Endocr. Rev.
Immune system development and function in prolactin receptor-deficient mice
J. Immunol.
Proapoptotic Bcl-2 relative Bim required for certain apoptotic responses, leukocyte homeostasis and to preclude autoimmunity
Science
The signaling domain of the erythropoietin receptor rescues prolactin receptor-mutant mammary epithelium
Proc. Natl. Acad. Sci. U. S. A.
The meaning of Scatchard and Hill plots
Methods Enzymol.
The roles of prolactin, growth hormone, insulin like growth factor-1 and thyroid hormones in lymphocyte development and function. Insights from genetic models of hormone and hormone receptor deficiency
Endocr. Rev.
Effects of prolactin deficiency on myelopoiesis and splenic T lymphocyte proliferation in thermally injured mice
Endocrinology
Role of interferon-gamma in counteracting the suppressive effects of transforming growth factor-beta 2 and glucocorticoids on the production of tumor necrosis factor-alpha
J. Leukoc. Biol.
Glucocorticoid–prolactin interactions in Nb2 lymphoma cells: antiproliferative versus anticytolytic effects
Proc. Soc. Exp. Biol. Med.
Cited by (17)
Chronic stress promotes oral cancer growth and angiogenesis with increased circulating catecholamine and glucocorticoid levels in a mouse model
2015, Oral OncologyCitation Excerpt :This leads to the stimulation of glucocorticoids (GC) secreted by adrenal cortex, which is essential for stress adaptation [8]. However, the plasma glucocorticoid level of tumor-bearing animals is similar to that of normal mice, and it may be argued that malignancy is a stressful condition leading to a reduction in circulating GC level [9–13]. Chronic stress is associated with dysregulation of HPA axis and LC/NE sympathetic system, leading an increase in the production of cortisol, as well as elevated level of NE and E.
Prolactin: Does it exert an up-modulation of the immune response in Trypanosoma cruzi-infected rats?
2011, Veterinary ParasitologyCitation Excerpt :Research dating from 1930s suggested a role for PRL in modulating the immune system (Smith, 1930; Kooijman et al., 1996). Later, several other papers demonstrated that PRL exhibits immunostimulatory properties (Yu-Lee, 1997; Clevenger et al., 1998) and up-regulates cytokine secretion and lymphocyte differentiation, especially in response to antigens and mitogens (Biswas et al., 2006). This is in addition to its ability to reverse glucocorticoid-induced immunosuppression (Kelley and Dantzer, 1991).
Prolactin and the skin: A dermatological perspective on an ancient pleiotropic peptide hormone
2009, Journal of Investigative DermatologyCitation Excerpt :PRL also abolishes the stress-induced inhibition of lymphocyte proliferation (Fomicheva et al., 2004) and increases cell sensitivity to the regulatory effects of IL-1 in the reaction of lymphocyte blast transformation. Furthermore, PRL prevents stress-induced T-lymphocyte apoptosis (De Mello-Coelho et al., 1998; Biswas et al., 2006). During the acute-phase response, PRLR expression is downregulated in various tissues, for example in liver, kidney, and lung, whereas PRLR expression in the thymus is upregulated (Corbacho et al., 2004).
Influence of Stress and Nutrition on Cattle Immunity
2007, Veterinary Clinics of North America - Food Animal PracticeCitation Excerpt :However, during chronic elevations of glucocorticoids, pre-B and pre-T cells experience accelerated programmed cell death (eg, apoptosis), which reduces the formation of lymphocytes, and causes atrophy of the thymus gland [91]. In mice, exogenous glucocorticoids decreased the cellular content and size of the thymus within 24 hours of injection [92], and induced apoptosis in normal immature thymocytes [93]. Similar results have also been reported in calves exposed to low doses of a synthetic glucocorticoid (dexamethasone) for extended periods of time, ranging from 14 to 25 days [94].