Chinese Hamster Ovary (CHO) cells are the most common mammalian cell line used around the world and are considered the “workhorse” for production of recombinant proteins in the pharmaceutical industry. Efforts have been made to optimise the production process through advancements in media formulation and improving process control strategies like bioreactor design, fed-batch feeding and temperature shift approaches, increasing batch titres from 50 mg/L to 5-10 g/L. However, it is believed that there is still room for improvement in the advent of media and process optimisation reaching a plateau. An alternative route to overcome this plateau is through engineering of the CHO host cells themselves. The overall aim of this PhD project was to identify and exploit endogenous CHO promoters to enhance heterologous protein expression. Having obtained ~ 30 CHO putative promoter sequences of varying length from 9 target genes from PCR, we screened and cloned 4 priority CHO promoter fragments into a variety of reporter vectors (GFP, Luciferase, p27 and EPO) to test their strength and utility. We have identified 3 novel temperature responsive promoters fragments from Cirbp SSu72 and Mdm2 genes and one constitutive promoter from a miRNA cluster [miR-17-92]. These promoters can permit moderate to high expression of a desired protein similarly to viral commercial ones such as cytomegalovirus (CMV) and simian virus (SV40) as well as boost expression levels of reporter proteins upon a temperature shift to 31oC. As a result, these novel tools are particularly advantageous in a bioprocess where reduced temperature is used already to increase protein production. In addition, we reported a ~94% decrease in clonal GFP stability of a CMV viral promoter versus our endogenous promoters over a 3 month timecourse experiment proving that viral promoters cannot sustain prolonged activity in culture like our novel endogenous promoter sequences. We have also shown that CHO clones overexpressing human XIAP exhibited 2/3-fold increased resistance to apoptosis and survival in extended culture settings compared to control cells. A secondary aim was to identify potential interacting miRNAs by utilising a novel pulldown method (miR-Capture), to isolate miRNAs targeting the anti-apoptotic XIAP mRNA in two different cell types, using a biotinylated anti-sense oligonucleotide capture affinity technique. Thus, identifying miRNAs which may impact on favourable phenotypes such as anti-apoptosis and increased growth rate may provide a means of improving CHO cell lines used for biopharmaceutical production. From the miR-Capture, there were 26 miRNAs detected in the human lysates and 14 in the CHO lysates. Four miRNAs (miR-124, miR-526b*, miR-760 and miR-877) were shown to be common from parallel CHO and human miR-Capture’s, using oligos designed against XIAP. Functional validation provided further evidence that miR-124 targets XIAP mRNA in CHO and human cells and may be a suitable target for miRNA engineering in CHO.