Not just a LTE case even same applies to UMTS also.
Say UE is trying to access google.com now google.com supplies the result of the search i.e. the downlink data. Now assume PGW/GGSN has assigned the address 10.1.1.1(private IP) to the UE, PGW address is 172.26.10.1 and Google.com address is 184.108.40.206
Now the packet with source IP as 10.1.1.1 and destination as google.com will reach to PGW (via LTE/UMTS network), now at PGW or any adjucent node 10.1.1.1 will be natted to a public IP which is assigned to to operator say 220.127.116.11 and will be forwarded to google.com, google.com will send the reply to the 18.104.22.168 as destination which will reach at PGW which will be reverse natted to 10.1.1.1 and Mobile network will drop it at UE.