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Heat shock protein families
Heat shock proteins comprise a large super-family of ubiquitously expressed highly conserved proteins present in all major cellular compartments in every organism from bacteria to human beings (Punyiczhi and Fésüs, 1998; Creagh et al., 2000). The Hsps are classified according to their molecular masses (kD) into different families including: Hsp110, Hsp90, Hsp70, Hsp60, Hsp40, and the small Hsp-family (Hsp28, Hsp27, and Hsp25). Some Hsps are not only stress inducible but are constitutively expressed, indicating a cellular function under normal conditions (Creagh et al., 2000). These include important housekeeping functions, for example, many stress proteins are molecular chaperones that help nascent polypeptides assume their proper conformation (Mallouk et al., 1999). Other essential functions include intracellular trafficking, antigen presentation, nuclear receptor binding, and regulating apoptosis (Jindal and Young, 1991). Furthermore, Hsps play important roles in the cell cycle, as well as in cellular differentiation and growth (Prohászka and Füst, 2004). The major Hsp families and their corresponding functions are summarised in Table 2.1.
Induction and regulation of the heat shock response
In eukaryotes, Hsp synthesis is regulated at the transcriptional level by the activation of the heat shock transcriptional factor (HSF-1) (Morimoto et al., 1994). In the unstressed cell, a chaperone complex (Hsp90, Hsp70, p60, FKB52, FKB51, CyP40 and p23) binding HSF-1 (Figure 2.4 – (1)), maintains it in an inactive form (Nair et al., 1996; Dorion and Landry, 2002).
During stress, Hsps become pre-occupied with the stress-induced unfolding and denaturation of native proteins resulting in the dissociation of the cytoplasmic chaperone/HSF-1 complex (Morimoto, 1993; Zou et al., 1998). In the process HSF-1 trimerizes and its nuclear localization signal is uncovered allowing its translocation and accumulation in the nucleus (Figure 2.4 – (2 & 3)). There it binds to a specific DNA sequence (-nGAAn-), referred to as the heat shock element (HSE) (Morimoto et al., 1994; Mallouk et al., 1999; Westerheide and Morimoto, 2005). This results in the activation of HSF-1 and Hsp gene transcription leading to an accumulation of Hsp expression (Freeman et al., 1999; Mallouk et al., 1999; Dorion and Landry, 2002) (Figure 2.4 – (4)).
Elevated levels of Hsps result in termination of Hsp transcription, and HSF-1 deactivation (Figure 2.4 – (5)), demonstrating that Hsps negatively regulate heat shock gene transcription via an auto regulatory loop (Craig and Cross, 1991; Hightower, 1991).
Hsps as mediators of apoptosis
Upon exposure to stressors, especially those associated with the protein machinery, certain Hsps are activated and expressed at high levels to protect the cell by maintaining protein homeostasis. It is this protective function of Hsps that leads to the suppression of several forms of cell death, including apoptosis (Beere, 2005). On the other hand, it has also been reported that Hsps do not exert the same effect on cell death under all conditions and in all models; it may either have no effect, inhibit, or enhance apoptosis (Vayssier and Polla, 1998). Activation of Hsps represents the functional endpoints of upstream apoptotic signals, making it extremely difficult to pinpoint the mechanisms that mediate the survival-/death-promoting effects of Hsps. Certain Hsps namely, Hsp 27, Hsp70, and Hsp90, have been implicated as modulators of PCD (Vayssier and Polla, 1998; Beere, 2005).
SECTION A: LITERATURE SEARCH
CHAPTER 1: BIOLOGICAL EFFECTS OF MOBILE PHONE RADIATION
1.1 INTRODUCTION
1.2 RADIO-FREQUENCY FIELDS FROM MOBILE PHONES – PHYSICS AND DOSIMETRY
1.3 BIOPHYSICAL INTERACTION OF RF-EMF WITH BIOLOGICALSYSTEMS
1.4 BIOLOGICAL EFFECTS OF RADIO-FREQUENCY FIELDS FROM MOBILE PHONES
1.5 STRESS RESPONSE AS A POSSIBLE PATHWAY FOR RFEMFEXPOSURE
1.6 REFERENCES
CHAPTER 2: MOLECULAR BASIS FOR CELLULAR STRESS: OCCURRENCE IN HUMAN SPERMATOZOA AND IMPLICATIONS FOR MALE FERTILITY
2.1 INTRODUCTION – GENERAL ASPECTS OF CELLULAR STRESS
2.2 BIOCHEMICAL CHARACTERIZATION OF APOPTOSIS
2.3 THEHEAT SHOCKRESPONSE: HEATSHOCK PROTEINS
2.4 CELLULAR STRESS IN HUMAN SPERMATOZOA
2.5 REFERENCES
SECTION B: THE EFFECT OF NON-THERMAL 900 MHz GSM MOBILE PHONE RADIATION ON HUMAN SPERMATOZOA
CHAPTER 3: CAPACITATION & OOCYTE BINDING
3.1 INTRODUCTION – MOLECULAR BASIS FOR CAPACITATION IN HUMAN SPERMATOZOA
3.2 RF-EMF EXPOSURE SYSTEM AND EXPERIMENTAL PROTOCOL
3.3 CAPACITATION: ASSESSMENT OF THE HUMAN MOTILITYAND THE ACROSOMEREACTION
3.4 HEMI-ZONA ASSAY
3.5 STATISTICALANALYSIS
3.6 RESULTS
3.7 DISCUSSION
3.8 REFERENCES
CHAPTER 4: APOPTOSIS
4.1 INTRODUCTION
4.2 EXPERIMENTAL PROTOCOL
4.3 ASSESSMENT OF THE APOPTOTIC STATUS IN SPERMATOZOA
4.4 STATISTICALANALYSIS
4.5 RESULTS
4.6 DISCUSSION
4.7 REFERENCES
CHAPTER 5: HEAT SHOCK PROTEIN & STRESS FIBRE ACTIVATION
5.1 INTRODUCTION
5.2 EXPERIMENTAL PROTOCOL
5.3 DETERMINATION OF HEAT SHOCK PROTEIN EXPRESSION AND PHOSPHORYLATION AFTER 900MHZ GSM RADIATION
5.4 PHYSIOLOGICAL EFFECTS OFHSPACTIVATION
5.5 STATISTICALANALYSIS
5.6 RESULTS
5.7 DISCUSSION
5.8 REFERENCES
SECTION C: CONCLUSIONS
CHAPTER 6: CONCLUSIONS AND RECOMMENDATIONS
6.1 CONCLUSIONS AND RECOMMENDATIONS
6.2 REFERENCES
SECTION D: ANNEXURES
