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HEAT SHOCK PROTEINS

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Heat shock proteins (HSPs) are a group of highly conserved proteins found in nearly all living organisms. They play a critical role in maintaining cellular homeostasis, particularly under conditions of stress such as heat, cold, UV radiation, and other environmental stressors. These proteins are part of a broader family known as molecular chaperones, which assist in protein folding, prevent protein aggregation, and promote the degradation of misfolded proteins. The discovery of HSPs can be traced back to the 1960s when Italian scientist Ferruccio Ritossa observed an unusual pattern of gene expression in Drosophila after exposure to elevated temperatures (Bose & Kim, 2020). This discovery marked the beginning of intensive research into the function and significance of these proteins.

In the context of cellular stress, HSPs are rapidly upregulated to protect cells from the damage that can be induced by protein denaturation and aggregation. When cells experience stress, proteins can lose their native structure, leading to misfolding or aggregation, which in turn can cause cellular dysfunction or death. HSPs mitigate this by binding to unfolded proteins and facilitating their refolding or directing them towards degradation pathways (Lindquist & Craig, 2021). HSPs thus play a vital role in maintaining the integrity of the proteome and ensuring cellular survival under adverse conditions.

The classification of HSPs is based on their molecular weight, and they are grouped into several families, including HSP100, HSP90, HSP70, HSP60, and the small heat shock proteins (sHSPs) (Li et al., 2019). Among these, the HSP70 family is one of the most well-studied and plays a crucial role in protein folding and protection against apoptosis. HSP90, on the other hand, is known for its involvement in stabilizing proteins that are critical for cell signaling, growth, and survival, making it an essential target in cancer research (Wang et al., 2021). These proteins not only protect cells from stress but are also involved in normal cellular processes such as signal transduction, cell differentiation, and immune response.

The regulation of HSPs is primarily controlled by heat shock factor 1 (HSF1), a transcription factor that becomes activated in response to stress. Under normal conditions, HSF1 is maintained in an inactive form in the cytoplasm, bound to HSPs. However, when cells are subjected to stress, HSF1 is released, migrates to the nucleus, and binds to heat shock elements (HSEs) in the promoters of HSP genes, initiating their transcription (Singh et al., 2022). This regulatory mechanism allows cells to quickly respond to environmental stressors by increasing the production of HSPs.

In addition to their role in stress response, HSPs have been implicated in various diseases, including cancer, neurodegenerative disorders, and cardiovascular diseases. For instance, elevated levels of HSP70 and HSP90 have been associated with cancer progression, as these proteins help in the stabilization of mutated oncoproteins and support the survival of cancer cells (Trepel et al., 2020). On the other hand, decreased levels of HSPs have been observed in neurodegenerative diseases like Alzheimer’s and Parkinson’s, where the inability to properly fold and clear misfolded proteins contributes to disease pathology (Kalmar et al., 2019). This dual role of HSPs in both protecting cells and

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